Approx. 1840 a Martin Grant m Elizabeth Neill. They had 7 children that I know of - (1) Mary Ann born 1841 - no marriage records for her. (2)James was born in 1842. In 1863 he married an Elizabeth Thompson - they had 4 children Agnes (1864), John Martin (1865), Michael (1867) and Thomas (1890). (3)Then William b 1845. He married Jane Kane Templeton in 1863. They had 5 children - Frances (1864), Matthew (1866), Eliza Jane (1876), David Ferguson (1878) and Robert (1883). (4) John b1850. He married an Eliz. Cooper in 1876. They had 6 children - David (1877), Grant (1881), Jemima (1883), Agnes Ferguson (1887), Hamilton Ferguson (1890) and John (1892). (5) Martin b1853. He married Mary Anne Gibson in 1873. They had 11 children. Mary Jane b 1873 (died), Andrew b 1875, Martin b 1878, Thomas b 1880, William b 1883 (HE WAS THE M.P.), George Gibson b 1885, Margaret b 1888, Samuel Linton b 1890 (my grandfather), Ebenezer b b1893, Eliza Neill b 1895 and Agnes Ferguson b 1901. (6) Elizabeth b 1855 - nothing known about her. (7) Agnes. In 1874 she married a David Hamilton Ferguson. They had 4 children - Hester (1885), Annie (1890), Adeline 1892, and Matthew (1894).
The difficulty I found to begin with was that it is a vast family. They have some names common to each branch of the family - Martin, William, Agnes Thomas, Ferguson, Hamilton etc. Fortunately my mother lived until she was in her late 90s and had a wonderful memory. Much of what she told me has greatly helped my research. 1911 census of Ireland - these addresses may help. 24 Chatsworth St Pottinger; 11 Glenrosa St Duncairn; 30 Mountcoyller Ave Duncairn; 19 Washington St Belfast East; 103 Mount collyer Road Duncairn; 33 Ruth St Duncairn - he was the M.P.
Information on William Grant M.P. can be obtained online view "The Stormont Papers"; "The Belfast Gazette" "William Grant Memorial Temperance Lodge"
Hope this helps some of you and the questions you asked.
June