Well if James Nixon's father was Thomas, chances are the following is an elder brother of James:
6 January 1828, John, son of Thomas Nixon of Kildoay, and Mary Hamilton
This baptism was in the record of Church of Ireland - Lower Cumber parish. Other Nixon entries in it are:
10 June 1812 Catherine, natural daughter of James Nixon & Mary Kerr
14 February 1844, Eliza, natural daughter of Thomas Nixon and Jane Craig
1 March 1848, Thomas, son of Adam Nixon, labourer, and Esther Hare
16 Jan 1865, Thomas, son of John Nixon, labourer of Goshoden, and Margaret Reed
Knockbrack townland is on the west side of Gosheden townland. Kildoag townland in on the southeast side of Gosheden townland.