Hi GPD
Welcome to Rootschat, you will find everyone really friendly and helpful here, I know I have.
I had a similar problem to yours, and one way to help narrow the parents down, is the naming tradition in Scotland.
Does David Dickson/Dixon's children or grandchildren have the same names as any of the suspect parents?
I have also found that the children some times have the Mother's or Grandmother's maiden name as a middle name, my own middle name is my Mothers maiden name and my cousin has our maternal Grandmother's maiden name, and my brothers middle names are from our GG Grandmothers.
Just a thought but it may narrow the search down a bit, especially if Oswald and Thomas were brothers or cousins, the wives name's would help to separate the two David's.
Yours Jane.