Hello Michelle,

If your Thomas QUILLIAM chr: 1840 Patrick - is in fact the one Frances suggests, he was an older brother to my grandmother - Elizabeth Anne QUILLIAM chr: 18 July 1852 Patrick.

Children to Joseph QUILLIAM and Anne SAYLE:
Jane (c) 26 Nov 1837 Patrick
Thomas (c) 29 Nov 1840 Patrick
Catherine (c) 10 Sept 1843 Patrick
Margaret (c) 20 July 1845 Patrick (?) died 1858
John Joseph (c) 30 July 1848 Patrick (not in 1851 census)
Joseph (c) 16 Dec 1849 Patrick
Elizabeth Anne (c) 18 July 1852 Patrick
Emily (c) 1 Jan 1855 Patrick

Joseph QUILLIAM'S birth father was a John QUILLIAM of Patrick, but I have not been able to identify which one to date, as there were a number of them in Patrick in the time-frame. Unless I can prove which John Q. it was, there is not much chance of getting back any further with this family line.
On the Parish Records Joseph is listed as (illeg) son of John Quilliam, but the next born William (1818) shows as "son of". However, I have never been able to find a marriage for John Q. and Catherine CHAMBERS.
Hope all this helps,
Marjery