Anne, this is an update.
James is not in the will of your Alex because he isn't his son. I now have the will of the correct Alex GRANT, patentee of Lot 15 W 1/2 2nd SSRR. He wrote his will in 1828 and it was proved in 1840. Children: James (inherits the Lot and is executor); John; Nancy (wife of Malcolm McDONALD); Catherine (wife of Donald McDONELL); Alexander, Duncan, Hugh.
I've just posted a speculative question about this family in another thread on this site, asking if the Alex and Anne in question could be the Donald Alexander GRANT and Nancy CAMERON named on a tombstone at St. Andrew's Williamstown.