I believe I can now say that Mary Ann Thorpe nee Nichols b circa 1816 was a daughter of William Nichols and Jane Costain. The crucial pieces of evidence are these:
*******
The presence of 2 Liverpool born siblings of Mary Ann in her 1851 household:
1851
82 Christian St, Islington, Liverpool
Ancestry's transcription:
Name Age
William Henry Thorpe 35
Mary Ann Thorpe 34
Henry Thorpe 7
Robert Thorpe 4
Margaret Thorpe 1
Abigal Thorpe 25
John Nicholls 24
Jane Nicholls 20
John Burrell 55
JN brother in law 24 unm house painter b LP
JN sister in law 20 unm laundress b LP
******
10 years earlier, John Nicholl and Jane Nicholl with their father, William and brother Joseph in Liverpool:
1841
Lancs, Liverpool, Mount Pleasant, district 20, image 17
Pembroke St
Ancestry's transcription:
Name Age
Wm Nicholl 50
Jno Nicholl 15
Joseph Nicholl 13
Jane Nicholl 12
WN 50 joiner N
JN 15 painter Y
JN 13 Y
Jane 12 Y
*******
And this from the IGI:
(Mary Ann Thorpe nee Nichols' youngest sister ?)
Name: Jane A Richards
Titles & Terms:
Event: Death
Event Date: 26 Dec 1910
Event Place: Boston,,Massachusetts
Residence:
Street Address:
Gender: Female
Age: 79
Marital Status: Widowed
Occupation:
Birth Date: 1831
Birthplace: England
Estimated Birth Year: 1831
Burial Date:
Burial Place:
Cemetery:
Father: William Nichols
Father's Titles & Terms:
Father's Birthplace:
Mother: Jane Costain
Mother's Titles & Terms:
Mother's Birthplace:
Additional Relatives:
Spouse: John Richards
Volume/Page/Certificate Number: 566
Film Number: 2313940
Frame Number:
Digital Folder Number: 4283171
Image Number: 02152
********
I couldn't find a baptism for Jane, but here's her brother John's IGI entry:
*******
Name: John Nichol
Gender: Male
Baptism/Christening Date: 15 Feb 1824
Baptism/Christening Place: Liverpool, Lancashire, England
Birth Date:
Birthplace:
Death Date:
Name Note:
Race:
Father's Name: William Nichol
Father's Birthplace:
Father's Age:
Mother's Name: Jane
Mother's Birthplace:
Mother's Age:
Indexing Project (Batch) Number: I00918-7
System Origin: England-EASy
Source Film Number: 93876
Reference Number: 195
**********************************
And this is brother Joseph, from his death record in Boston, Mass:
Name: Joseph J. Nicholls
Titles & Terms:
Event: Death
Event Date: 15 Dec 1892
Event Place: Boston, Suffolk, Massachusetts
Residence: Boston, Mass
Street Address: 52 Walnut St
Gender: Male
Age: 64
Marital Status: Married
Occupation: House Painter
Birth Date:
Birthplace: England
Estimated Birth Year: 1828
Burial Date:
Burial Place:
Cemetery:
Father: William
Father's Titles & Terms:
Father's Birthplace: Isle of Man
Mother: Jane Costain
Mother's Titles & Terms:
Mother's Birthplace: Isle of Man
Additional Relatives:
Spouse:
Volume/Page/Certificate Number: P 464
Film Number: 961508
Frame Number:
Digital Folder Number: 4225003
Image Number: 490
******
I have lots more notes on their Manx born siblings which I'll paste below, but it's not in any particular order---just copied and pasted as I came across it whilst looking for strong evidence linking Mary Ann to parents William Nichols and Jane Costain. The initial search was in Liverpool Marriages and Banns for people with a surname Nichols whose father was William Nichols, joiner.
******
Marriage of Mary Ann's parents:
Groom's Name: Wm. Nichol
Groom's Birth Date:
Groom's Birthplace:
Groom's Age:
Bride's Name: Jane Costain
Bride's Birth Date:
Bride's Birthplace:
Bride's Age:
Marriage Date: 14 Sep 1813
Marriage Place: Braddan,Isle Of Man,England
Groom's Father's Name:
Groom's Mother's Name:
Bride's Father's Name:
Bride's Mother's Name:
Groom's Race:
Groom's Marital Status:
Groom's Previous Wife's Name:
Bride's Race:
Bride's Marital Status:
Bride's Previous Husband's Name:
Indexing Project (Batch) Number: M03802-1
System Origin: England-ODM
Source Film Number: 106188, 106189, 106190, 106708, 106709, 106710, 106711
Reference Number:
******
Marriage of Mary Ann's brother:
Liverpool, Lancashire, England, Marriages and Banns, 1813-1921
about John Nicholls
Name: John Nicholls
Age: Full Age
Marriage Date: 2 Oct 1853
Parish: Liverpool St Nicholas
Spouse's Name: Jane Williams
Father's Name: William Nicholls
Spouse Father's Name: John Grigson
JN/full age/widower/painter/Roscoe St/father William Nicholls, joiner.
JW/full age/widow/Hotham St/father John Grigson, marine store dealer.
Witnesses: John Wynn and Sarah Wynn.
*******
Mary Ann Thorpe's brother, John Nicholls with wife Jane alias Williams nee Grigson and Jane's children from her first marriage:
1861
Brownlow Hill, Mt Pleasant, LP
Ancestry's transcription:
Name Age
John Nicholes 35
Jane Nicholes 36
Elizabeth Williams 17
Mary J Williams 15
John Williams 13
William J Nichols 7
Eliza A Nichols 5
Louisa Nichols 1
*******
Name: John Nichol
Gender: Male
Baptism/Christening Date: 15 Feb 1824
Baptism/Christening Place: Liverpool, Lancashire, England
Birth Date:
Birthplace:
Death Date:
Name Note:
Race:
Father's Name: William Nichol
Father's Birthplace:
Father's Age:
Mother's Name: Jane
Mother's Birthplace:
Mother's Age:
Indexing Project (Batch) Number: I00918-7
System Origin: England-EASy
Source Film Number: 93876
Reference Number: 195
**********************************
A brother of Mary Ann ?
Liverpool, Lancashire, England, Marriages and Banns, 1813-1921
about William Nicholls
Name: William Nicholls
Age: Full Age
Marriage Date: 13 May 1845
Parish: Richmond St Anne
Spouse's Name: Elizabeth Bowdler
Father's Name: William Nicholls
Spouse Father's Name: Edward Bowdler
WN/full age/bachelor/butcher/Christian St/father William Nicholls, overseer.
EB/full age/spinster/Christian St/father Edward Bowdler, labourer.
Witnesses: Henry Tullock ? and Letitia Sandler ?
******
Liverpool, Lancashire, England, Marriages and Banns, 1813-1921
about Thomas Nichols
Name: Thomas Nichols
Age: Full Age
Marriage Date: 8 Oct 1838
Parish: Liverpool St Peter
Spouse's Name: Ann Gardner
Father's Name: William Nichols
Spouse Father's Name: Solomon Gardner
TN/full/bach/painter/Peach St/father William Nichols, joiner.
AG/minor/spinster/Peach St/father Soloman Gardner, waiter ?
Witnesses: Carson Smith and Catharine Gardner.
******
1841
Cheshire, Birkenhead, district 1, image 2
Tory ? Place
Thomas Nicholls 20 painter N
Ann 20 N
William 2 Y
******************
1851
Cheshire, Birkenhead, 1f/7
Monks St
Ancestry's transcription:
Name Age
Thomas W Nichols 32
Ann Nichols 32
William Nichols 11
Thomas Nichols 8
Ann J Nichols 6
John Nichols 4
Mary Nichols 3
Joseph Nichols 2
Joseph Nichols 1 Mo
Sarah Jones 26
TWN painter and plumber b LP
AN wife b Preston
children b Birkenhead, LP and Tranmere.
The 1 month old is a daughter, not yet named.
*******
1861
Lancashire, Liverpool, St George 9/33
12 School Lane
Ancestry's transcription:
Name Age
Thomas W Nichols 42
Ann Nichols 42
Thomas Nichols 19
Ann J Nichols 16
John Nichols 14
Joseph Nichols 10
Mary Nichols 12
Margaret Nichols 7
Robert Nichols 2
Martha M Nichols 11 Months
TWN painter emp 2 men/2 ap / b DOUGLAS, IOM
AN wife b Preston
Chn b LP+Tranmere
******
Liverpool, Lancashire, England, Baptisms, 1813-1906
about Ann Jane Nichols
Name: Ann Jane Nichols
Baptism Date: 24 Nov 1844
Parish: Liverpool St Peter
Father's Name: Thomas Nichols
Mother's Name: Ann Nichols
Address, Birkenhead, Cheshire, father's occupation--painter.
******
Liverpool, Lancashire, England, Baptisms, 1813-1906
about Mary Jane Nichols
Name: Mary Jane Nichols
Baptism Date: 20 Sep 1841
Parish: Liverpool St Peter
Father's Name: Thomas Nichols
Mother's Name: Ann Nichols
Birkenhead, Cheshire, painter.
*******
Liverpool, Lancashire, England, Marriages and Banns, 1813-1921
about Margaret Nichols
Name: Margaret Nichols
Age: Minor
Marriage Date: 7 Oct 1839
Parish: Liverpool St Peter
Spouse's Name: Robert Davies
Father's Name: William Nichols
Spouse Father's Name: Robert Davies
RD/full/bach/cooper/St Andrew St/father Robert Davies, cooper.
MN/minor/spinster/St Andrews St/father William Nicholls, joiner.
Witnesses: John White and Emma White.
*******
1841
Trowbridge St, Red Lion Place, Mount Pleasant, LP
John White 25 tailor journeyman N
Emma 25 Y
Elizabeth 1 Y
Margaret Davies 20 Y
Robert Davies 25 cooper journeyman Y
James 4 Y
******
Possibly a brother of William Nichols, joiner ?
Liverpool, Lancashire, England, Marriages and Banns, 1813-1921
about Edward Nichol
Name: Edward Nichol
Marriage Date: 8 May 1830
Parish: Liverpool Christ Church
Spouse's Name: Ann Gill
EN bachelor, joiner
AG spinster
witnesses: Jos ? Nichols and Thomas Robertson.
*******
1851
1 Gordon St, Everton
Edward Nichool (sic) 47 head mar joiner b IOM
Ann Nicholl wife 35 housekeeper b IOM
Margaret dau 10 b LP
Thomas son 7 b LP
*******
Mary Ann not long before her death:
Ancestry's transcription:
1901
Lancashire, West Derby, WD Western, 20/30
1 Odsey St
Ancestry's transcription:
Name Age
William Beaman 47
Elizabeth Beaman 41
William H Beaman 21
Ernest J Beaman 9
Alfred Beaman 6
Edith M Beaman 4
Erie Beaman 1
Mary A Thorpe 85
Emily J Williams 23
EB 41 teacher of pianoforte
MAT 85 m in law b LP
******
Ancestry's transcription of Mary Ann's daughter Elizabeth Thorpe's marriage:
Liverpool, Lancashire, England, Marriages and Banns, 1813-1921
about Elizabeth Shorpe
Name: Elizabeth Shorpe
Birth Year: abt 1857
Age: 19
Marriage Date: 13 Sep 1876
Parish: Liverpool St Bride
Spouse's Name: William Joseph Beaman
Father's Name: William Henry Shorpe
Spouse Father's Name: William Beaman
WJB/full age/bachelor/joiner/14 Morpeth St/father William Beaman, warehouseman.
Elizabeth Thorpe/19 years with consent/spinster/14 Morpeth St/father William Henry Thorpe deceased.
Witnesses: John James Biggar and Elizabeth Percival.
*******
1891
Name Age
William I Beaman 37
Elizabeth Beaman 31
Wm H F Beaman 11
William J Beaman joiner b LP
EB 31 professor of music b LP
WHFB son
*******
Possible death entry for Mary Ann (registered by someone who guessed her birth year ?)
*******
England & Wales, FreeBMD Death Index: 1837-1915
about Mary Ann Thorpe
Name: Mary Ann Thorpe
Estimated Birth Year: abt 1822
Date of Registration: Apr-May-Jun 1902
Age at Death: 80
Registration district: West Derby
Inferred County: Lancashire
Volume: 8b
Page: 407
*******
Jean C