So we now know William had Brothers Alexander and George at least.
This may be Georges Marriage;
9 July 1815, Marnoch Church, Marnoch
George GRANT/Elspet SIMPSON
No Witnesses named
Possible 1861 Census, Alvah, Banffshire;
Civil Parish: Alvah
County: Banffshire
Address: Walkmill
George GRANT, 69 (1792) Farmer Of 15 Acres, born Alvah
Elspet, 70, Wife, born Rothiemay
Mary, 43, Daug, Dressmaker, born Alvah
Anna, 37, Daug, born Alvah
1871 George says he is born Gamrie
1841 we have;
George Grant 45
Elspit Grant 50
Jane Grant 25
Annah Grant 15
Yes that is them in Census Baptisms on FreeREG;
ANNA, 16 Aug 1823 in Alvah
JAMES, 14 Oct 1815 Marnoch
JANE, 14 Oct 1815 Marnoch
Mother Elspet SIMPSON