I am sorry Frances to have got you into a state of confusion!
My Husband's2xGGrandfather was William Costain b1812, s/o Richard and Jane Duke.
William's daughter Jane was related to the historical author Thomas B Costain, s/o John and Ann Duke. Both of them living near by each other in Canada.
I am trying to find the connection between Richard and Jane, and John and Ann. I will then be able to find the Cousin relationship(2nd, 3rd, 4th etc)
I had hoped a marriage doc for John/Ann would have his parents?
So as you see Ann Duke is only a relation by marriage to a cousin.
I am sorry I had not made it clear the first time, I hope this is better.
Thanks anyway,
Penny