Why two Janets? Consider the possibility that Janet II is the blood-niece of Janet I, and that she and David Edney are first cousins.
1st Gen: John Robertson = Janet Blyth
2nd Gen: a) Margaret Ritchie = James Rob_n & b) Janet Rob_n = William Edney
3rd Gen: a) Janet Robertson ============= b) David Edney
However, could not find a baptism for a James Robertson to a John & Janet in the right place/time. Anyone have other ideas?
I know it's a basic effort, but can only find one Janet Robertson baptised in Ferryport around the right time which might place her in a position to marry William Edney. It's a 1747 baptism to parents John Robertson & Janet Blyth at Ferryport on Craig.