Hi Jen,
When you say you've had DNA links to the Dewar family, can you establish exactly what link? e.g. have you matched with a possible second cousin or similar? Have you made contact with them? Perhaps there are some family stories there. You would presumably be looking to establish which of their relatives are potential candidates (men of an age to father a child in 1940, especially those who were in the military and may have been in the Watford area)
The more closely related people you can get to do a DNA test with you, the easier it will be to narrow it down, e.g.:
- your father's half-siblings on the Sturgess side, if any, or their children - this gives DNA links to your father's mother, but not his father, which helps in ruling out other connections.
- anyone on the Dewar side, particularly those directly descended from any potential candidates.
For example, consider this hypothetical family structure:
There are two brothers, Thomas and William Dewar, and a sister Mary Dewar, who are all full siblings.
You have matched with a grandchild of Mary Dewar, and the degree of match suggests that either Thomas or William could be your grandfather. Both Thomas and William married after the war and have living children/grandchildren. You find a grandchild of Thomas willing to do a DNA test.
If one of these men was your grandfather, then Mary Dewar was your dad's aunt, her children are your father's first cousin, and her grandchildren are your second cousins.
If Thomas was your grandfather, his children are your father's half-siblings, his grandchildren are your half cousins. You will on average have twice as much DNA in common with Thomas' grandchildren than with Mary's grandchildren.
On the other side, if Thomas was not your grandfather, and William was, then your match to Thomas' grandchildren will be about the same as with Mary's grandchildren. (There may be other possible explanations depending on the various levels of DNA matches).
jorose
