My brain is hurting.
From where did the information come that Janet Paton's husband John Beaton had an earlier marriage to Flora Paton and a son called William Pollock? It is really actually remarkable to find that if John Beaton's father WAS Alexander he did not call his eldest son or ANY of his several sons Alexander. Assuming it is a fact that Janet Paton did have a stepson called William Pollock Beaton, is it possible - in fact I can answer that straightaway and say yes it is - that the person submitting information about William Pollock Beaton to Ancestry has simply got it wrong, and given the wrong John Beaton as Dad to William Pollock.
The Ancestry trees are always interesting, as long as one remembers that they sometimes do get it terribly wrong.
In any case William Pollock's dad is likely to have been born BEFORE 1813 to tie in with Flora's age and the fact that he died 10 years before Janet Paton. It doesn't follow for sure - of course not - but it is quite likely.
I will look into possible family connections between Flora's father, James Paton, and Janet's father, John Paton, remembering all the while that there is now a possibility Janet's father was called George!.