Enjoying the links and the reading the material, Malcolm.
Hopefully someone can confirm William 1837's birth and parents details from his marriage to Marion Grant. This will let you all make the definite connections.
Going back to the beginning, I would agree with Ev that very likely William's parents' were William and Jane
https://familysearch.org/pal:/MM9.1.1/XTRX-894 Lots of children show for them
https://familysearch.org/search. Mother Jane's surname with a number of variants such as Ainsley/Emslie/Emsley etc.
1851 census here - all the children born in Canongate:
William Forsyth 47 labourer b. Ardersier, Invernesshire
Jane Forsyth 34 b. Aberdeen
Ann M Forsyth 17
William Forsyth 14
John Forsyth 11
Jane Forsyth 8
Alexander Forsyth 6
Eliza Forsyth 4
Andrew Forsyth 3
Mary Forsyth 1
Address: Abbey Court, Edinburgh Canongate
Edinburgh Parish Register records are some of the best in that pre 1855 era and the start of official registration. Parish Register entries mostly have very little info, pretty much no more than just names. However, for William and Jane's marriage, the entry includes Jane's father too
https://familysearch.org/pal:/MM9.1.1/XT1G-W7CWith my guessing hat
, wonder if John Grant F's twin, Alexander may have been called after maternal grandfather and the 'A' middle name might be a variant of Ainsley? Scottish naming pattern, if used and it often was, can be a useful guide (see here for example
www.halmyre.abel.co.uk/docs/Family/naming.htm).
Monica