I have been looking at this family in Glasgow for 1901 who are lodging at the household of a David Darroch. They all show as born in Ireland except youngest, Frederick, who was born in Glasgow:
Margaret Gallacher 48 widow Tailors Remnant Sorter b. Tyrone
John Gallacher 14 Corporation Trace Boy
Susan Gallacher 10 b. Donegal
Paul Gallacher 7 b. Tyrone
Fredk Gallacher 3 b. Glasgow
Address: 57 Breadalbane St, Glasgow/Kelvin
I can trace this family back to Ireland and son John was born on 1 March 1887 (I know you have a date of 13 March 1887)
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1887/02568/1949586.pdfThe sticking point is that husband/father was called Patrick not Denis. Patrick looks to have died between 1897-1901. I think he may have died in 1898 and was buried at Dalbeth.
A lots fits overall. It just the issue on Patrick/Denis that makes me more hesitant.
Haven't found the death of Margaret Devlin/Gallacher so far. There is one in 1905 but different husband's name (John) and father's name doesn't match details on her 1871 marriage
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1871/11332/8159254.pdfJust making a note of this to see whether you or any other researchers had looked at this family?
Monica