Can you give us some sort of PoD to work on?
I mean, to prevent their rise to the English throne, then there are any number of potential PoDs in the Tudor period: Henry VII has more sons, Arthur Prince of Wales survives, Henry VIII has more sons, Edward VI is healthy, Mary or Elizabeth have children...
However, none of these prevent a Stewart accession to the Scots throne, seeing as this happened nearly 250 years before James VI & I. To prevent this one, you need to keep some of the Bruce family alive and kicking. Maybe Edward Bruce doesn't die in Ireland, or David avoids capture at Neville's Cross, and so doesn't spend years stuck in England, instead fathering many children North of the border.
But seriously Pericles, what's with the dozens of questions.