There are RC baptisms for the two Margarets who died in the 1860s to Samuel and Margaret. There are also C of E baptisms for each Margaret. By the way Margaret's surname here is Wright so they did marry on the island in 1848.

Name: Margaret Ann Stewart
Event Type: Christening
Event Date: 30 Oct 1860 privately baptized
Event Place: Ballaugh, Isle of Man
Father's Name: Samuel Stewart, labourer
Mother's Name: Margaret Wright
Abode: Kirk Michael Ballaugh
Link: familysearch.org/ark:/61903/1:1:XZ1M-X92

Name: Margarita Anna Stuart
Event Type: Christening
Born: 03 Nov 1860
Event Date: 06 Aug 1861
Event Place: Douglas, Isle of Man
Father's Name: Samuelis Stuart
Mother's Name: Margarita Wright
God Mother: Joanna Murphy
Link: familysearch.org/ark:/61903/1:1:XZ1K-PXD

Name: Margaret Stewart
Event Type: Burial Event
Date: 17 Nov 1862
Event Place: Malew, Isle of Man
Age: 2
Birth Year (Estimated): 1860
Abode: Malew Street
Link: familysearch.org/ark:/61903/1:1:XZTL-MY3

Name: Margaret Stewart
Event Type: Christening
Event Date: 07 Dec 1863
Event Place: St Barnabas, Braddan, Isle of Man
Father's Name: Samuel Stewart, Labourer
Mother's Name: Margt Stewart
Abode: Douglas
Link: familysearch.org/ark:/61903/1:1:XZBC-YHF

Name: Margarita Stewart
Event Type: Christening
Born: 07 Dec 1863
Event Date: 10 Jan 1864
Event Place: Douglas, Isle of Man
Father's Name: Samuelis Stewart
Mother's Name: Margarita Wright
God Mother: Joanna Collins
Link: familysearch.org/ark:/61903/1:1:XZ1K-B99

Name: Margt Stewart
Event Type: Burial
Event Date: 22 Dec 1864
Event Place: Braddan, Isle of Man
Age: 1
Birth Year (Estimated): 1863
Abode: Douglas
Link: familysearch.org/ark:/61903/1:1:XZT9-RNY