According to my notes, Robert Stephen Moore did have a sister Elizabeth Eleanor, but she was baptised in 1865 and although I have a note that she died, I don't know what happened to her. His eldest sister Margaret Jane Moore seems to have married her cousin Robert Moore. Below is some of what I have compiled about this family, often taking my lead from previous messages on this board, including from Jim Moore. What I haven't done is checked the parish register entries where it states 'IGI' or 'Lawson' which would give better evidence to prove the case. RS Moore was the nephew of my gg grandmother Elizabeth Cavendish nee Moore
Margt Jane Moore c. 29 Dec 1861 Braddan d. Robt Moore & Jane Cowley IGI
Cathne Ann Moore c. 26 Jun 1863 Braddan, d. Robert Moore & Jane Cowley IGI
Elizth Eleanor Moore c.12 Feb 1865 Braddan (D:28 Feb 1865) d. Robert Moore & Jane Cowley IGI
Robert Stephen Moore c.7 Oct 1866 Braddan s. Robert Moore & Jane Cowley IGI
1871 census has:
Catherine Ann with cousins William & Catherine Quiggin
1871 Shalghage, Michael RG10/5772 f.60 p.10 sch.10
William Quiggin - h - m - 60 - Land owner - KK Michael
Catherine - w - m - 40 - KK Michael
Catherine A Moore - Cousin - 7 - Scholar - Douglas
Margaret Callister - servt - 16 - Domestic servant - KK Michael
Robert Stephen with aunt/uncle Richard & Elizabeth Cavendish
1871 26 St George’s Walk, Douglas RG10/5776 f27 p15 sch ED1
Richard Cavendish - H - m - 46 - Carter - Ballaugh
Elizth - w - m - 45 - - Peel
Tho. R. - s - 25 - Carter (Carrier?) - Michael
Ann - d - 20 - Housekeeper - Michael
Margt - d - 13 - scholar - Douglas
Cath J. - d - 11 - - “
Elizth - d - 7 - - “
Edith Ellen - d - 4 - - “
Robt S. Moore - nephew - 5 - - “
MOORE, Robert Stephen married KAY, Elizabeth Ann 25 May 1889 D dsg 23b [Lawson]
Margaret Jane with grandparents Daniel & Elizabeth Cowley
1871 Ardwhalan, Braddan RG10/5777 f51 p6 sch26
Daniel Cowley - h - m - 58 - Farmer 50 acres - Braddan
Elizabeth - w - m - 60 - Farmer wife - “
John - s - un - 23 - Farmer - “
Thomas - s - “ - 19 - “ - “
Robert - s - “ - 11 - “ - “
Ann - d - “ - 30 - “ - “
Catherine - d - “ - 27 dressmaker - “
John ?F Christian - Grandchild - 12 - scholar - Braddan [f52 p7]
Margaret J Moore - “ - 9 - scholar - “
MOORE, Margaret married MOORE, Robert 10 Feb 1900 D bra 796b [Lawson]
Margt Jane d/o Robt Moore & Jane Cowley c. 29 Dec 1861 Braddan IGI
Robert s/o William Moore & Eleanor Bell c.28 Apr 1861 KG IGI ext
(1871) Ballavarkish, German RG10/5771 f.126-127 p.14-15 sch.62
William Moore - h - m - 40 - Farming 50 acres - German
Eleanor - w - m - 38 - - Braddan [Bell]
William T - s - u - 18 - - German
Eleanor J. - d - u - 15 - - German
Ann - d - - 11 - scholar - German
Robert - s - 10 - scholar - German [1861]
Elizabeth - d - 7 - scholar - German
Eliza - d - 5 - - German
John J. - s - 3 - - German
Margaret - d - 5mo - - German
MOORE, Robert William 1 Jul 1900 Dou s/o MOORE, Robert & MOORE, Margaret [Lawson]
(1901) 9 Well Road Hill, Douglas RG13/5303 f.145 p.9 sch.58
Robert Moore - h - m - 40 - Car proprietor - German
MARGARET - w - m - 39 - - Douglas
Robert W. - s - 9mo. - - Douglas
?MOORE, Robert William 59 buried Douglas Borough Cemetery 23 Oct 1959 [Lawson]
I would just repeat that this is merely put together from indexes and censuses, seems to work, but I would also welcome verification.