I have Lydia on IGI and 1850 census, and have the mother living alone in Bangor in 1870 census.In any event, the link to John runs like this (It is easily run from Tristram to Abner using the white Coffin Ancestry book):
Abner Coffin (Mary Rawlings) b. Newbury 29Apr1702, d. Freeport 1763.
Stephen Coffin (Martha Chapman) b. 6Jun1744, d. Freeport 29Aug1800.
John Coffin(Dorcas Griffin) b. Lewiston 12Jun1780, d. Webster 16Aug1845.
John Coffin (Sarah ?) b.Webster 1Feb1806 d. ?
**Webster is now Sabattus.If Lydia is our person, then at least the marriage age of 16 would be more acceptable.