Marriage in 1891 for Edward’s son William John to Mary Ann O’Kane. Note he was a widower. I can’t see his first marriage in Irish records. I think his first marriage may have been in the USA.
https://www.irishgenealogy.ie/files/civil/marriage_returns/marriages_1891/10666/5886831.pdf
Birth of a daughter Margaret to that couple in 1895:
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1895/02209/1834375.pdf
They also had a son Edward Joseph in 1893 (birth was registered 2 years late, in 1895).
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1895/02209/1834376.pdf
Son Thomas James born 1897 by which time the family had moved to Bellagherty:
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1898/02099/1799971.pdf
Son Francis Patrick born 1899
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1899/02055/1786343.pdf
There were other children, including Isabella Edith and John. Here’s the family in the 1901 census in Bellagherty:
https://www.census.nationalarchives.ie/pages/1901/Londonderry/Salterstown/Bellagherty/1533522/
Note that Annie Mary was born in the USA c 1888, indicating William John had been living there at that time. He obviously returned to Ireland by 1891 as he married Mary Ann that year. William John is missing from the 1901 census. Presumably in the USA as he died there in 1903. Probate abstract:
Administration of the estate of William John M'Callion late of Bellagherty County Londonderry Farmer who died 2 July 1903 at Port Washington Long Island U.S.A. granted at Londonderry to Mary Anne M'Callion the Widow.
Family in the 1911 census:
https://www.census.nationalarchives.ie/pages/1911/Londonderry/Salterstown/Belagherty/614225/
Possible death for Mary Anne McCallion on 7th August 1935, registered in Magherafelt. That's not viewable on-line free. It's pay to view on the GRONI site.
I spotted this death in 1889 for an Edward McCallin, merchant, who lived in Coagh, Co Tyrone. William John also lived in Coagh when he married and was also a merchant. I’d guess they were brothers.
https://www.irishgenealogy.ie/files/civil/deaths_returns/deaths_1889/06144/4755420.pdf
Another sibling here. James McCallin died in 1887 aged 20. Informant was his father Edward of Ballyloughan.
https://www.irishgenealogy.ie/files/civil/deaths_returns/deaths_1887/06208/4776064.pdf