Hullo again!
Grange's Pew Allocation of 9 Jun 1704 shows but one Bruce: "Alexander Bruce in Edingight".
He must have been the "Alexr Bruce in Edingight" who was a witness on 12 Sep 1704; even possibly he was named on 11 Aug 1691 too. "Alexr Bruice elder and younger in Edingight" were witnesses on 21 Jul 1709 to a child of John Bruce & Margaret Wilson (named Alexander). It is reasonable to suggest that Alexander Bruce elder was the father of both Alexander Bruce younger and John Bruce.
On 1 Sep 1713, "Alexander Bruce" was witness to a child of George Bruce & Margaret Allan (named Alexander). It's reasonable to suggest that not only this is Alexander Bruce younger but also his father had died by then.
The name Thomas Bruce never turns up in the context of these families.
So, whilst undoubtedly Thomas Bruce & Margaret Robertson had a son George in Grange (in 1685), it does look as though an Alexander Bruce in Edingight was around and stayed around having a family too. With a Thomas Bruce conveniently turning up in Portsoy by 24 Mar 1688 (obviously if he had come from Grange, their son George would have been with them, had he survived), the balance of evidence, albeit inconclusive, is that George Bruce (h/o Margaret Allan) is son of Alexander, not Thomas.
Thomas, whether in Grange or in Portsoy, was most certainly not the Earl of Elgin! Oddly enough, Hon Thomas Charles Bruce (1825-1890), who was son of the 7th Earl of Elgin, is a key player in a talk I'm giving next week on Friday 13th in Blair Castle about the 150th anniversary (9 Sep 2013) of the opening of the Highland Railway between Inverness and Perth: he was Chairman of the Inverness-based railways involved.
I looked at all the early Bruce baptisms in the early Fordyce OPR. The few places mentioned do not suggest anything other than that these Bruces were artisans (most in Portsoy, but some in Muir of Glassaugh, in Cowhythe, in Redhythe etc). However, one of them has the unique (for Fordyce and Grange) forename of Michael - the only person so named in the whole of the Fordyce and Grange OPRs to 1855. He had a brother Peter/Patrick. Both these names (only the names, mind you) are connected with the Bruces of Airth and Stenhouse, and it's these Bruces that descendants of John Bruce in USA are apparently claiming as ancestors, albeit with Stenhouse consistently misnamed as Sterlinghaus.
I decided enough was enough! These Fordyce Bruces are right at the beginning of the OPR, seemingly by then well-established in the parish, artisans not landowners, so until there's evidence to suggest the contrary, they are local and the trail ends there.
As for your thrice-married William Bruce, he's separate from all this. But there is a fitting William Bruce bpt 11 May 1684 Grange to George Bruce & mother Shearer. You could concoct all sorts of viable scenarios involving every known Bruce in Grange - and who knows? - one might be right!