Hoped to have found a bit more but here are some bits and pieces-
Isabella McGlynn ?(c1864 Belfast-aft.1898/1901)
In 1901 census there's a female listed as I McG, age 37, RC, born Belfast, single in the Workhouse-
https://www.census.nationalarchives.ie/pages/1901/Antrim/St__George_s_Ward_Belfast/Lisburn_Road/966799/ Could this be the mother Isabella?
1. ? Thomas McGlinn (1881 Belfast)
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1881/02819/2034202.pdfCan’t find marriage of death in Belfast, can’t find in 1901 census.
2. ? Elizabeth McGlynn (25 May 1886 Workhouse)
a.? Kathleen McGlinn (1911)
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1911/01521/1617573.pdf3.
Mary McGlynn (24 Oct.1887 Workhouse)
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1887/02541/1940717.pdf4.
Isabella McGlynn (24 Oct.1887 Workhouse) m.(1905) Edward Clarkin; m.(1914) Henry Cullinan
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1887/02541/1940717.pdfhttps://www.census.nationalarchives.ie/pages/1901/Antrim/Whitehouse/Lr__Whitehouse_Street/988400/ (boarder Bella McGlinn, 13, Co.Antrim, RC, linen doffer mill worker)
https://www.irishgenealogy.ie/files/civil/marriage_returns/marriages_1905/10179/5703704.pdf (bride's residence Whitehouse & father John McGlynn (dead))
Edward & Isabella Clarkin in 1911 with two sons-
https://www.census.nationalarchives.ie/pages/1911/Antrim/White_Abbey/Carson_Street/190665/Isabella's 2nd marriage in 1914-
https://www.irishgenealogy.ie/files/civil/marriage_returns/marriages_1914/09854/5578733a.pdfhttps://www.irishgenealogy.ie/files/civil/marriage_returns/marriages_1914/09854/5578733.pdf (her father John McGlynn, sailor)
5.
Annie McGlynn (6 June 1890 Workhouse) m.(1913) Bruce Wallace Morton
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1890/02433/1905917.pdfhttps://www.census.nationalarchives.ie/pages/1901/Antrim/Whitehouse/Lr__Whitehouse_Street/988400/ (boarder Annie McGlinn, 10, Co.Antrim, RC, scholar)
https://www.census.nationalarchives.ie/pages/1911/Antrim/Whitehouse/Cahoon_s_Street/191182/ (boarder Annie McGlynn, 21, Co.Antrim, RC, linen reeler)
https://www.irishgenealogy.ie/files/civil/marriage_returns/marriages_1913/09869/5585034.pdf 6.
Agnes McGlynn (c1895/c1893 Belfast-aft.1911)
https://www.census.nationalarchives.ie/pages/1901/Antrim/Whitehouse/Lr__Whitehouse_Street/988400/ (boarder Agnes McGlinn, 6, Co.Antrim, RC, scholar)
https://www.census.nationalarchives.ie/pages/1911/Antrim/Whitehouse/Cahoon_s_Street/191182/ (boarder Aggie McGlynn, 18, Belfast City, RC, linen spreader)
Belfast City, RC, linen spreader)
7.
Margaret McGlynn (7 July 1898 Workhouse-6 Feb.1979 Cork) m.(2 Jan.1922 Belfast) John Patton
https://www.irishgenealogy.ie/files/civil/birth_returns/births_1898/02076/1792449.pdf Other than possible entry in 1901 census there is no sure sighting of mother Isabella after birth of daughter Margaret in 1898. I can't find any marriage or death for her from 1898-1921 Irish Genealogy). I then continued searching for a death after 1921 on PRONI and found her death! (I downloaded the registration so contact me if you'd like a copy)
13 Nov.1932 at 51 Lisburn Rd., Belfast,
Isabella McGlynn, late of Vere Street, spinster,
age 78, millworker, chronic bronchitis certified,
informant Isabella Cullinan daughter in attendance 3 Ypres Park Whiteabbey.
This puts Isabella's born about 1854 but may not be accurate.