It shows Mindwell is indeed a sibling, but unfortunately no first wife.Like I said, I have no documentation to prove it - just speculation so far on my part, based on the name connections and the connection to the STEVENS family.
Susannah WALKER's birth in 1739 fits the timeframe fairly well- about 34 years old at Joel F.'s birth (1763),35 years at Mindwell's (1764).
I am guessing Susannah WALKER-Moore died after Matilda was born (1765) and Joel Sr. sent the (also undocumented) first daughter Susannah to live with the STEVENS family (her aunt & uncle if my theory is correct).
If I find something, I will let you know. (Hope you will do likewise!)
I don't see a connection to the ATWOODs, was Mercy a child of Stephen & Mindwell's?It is interesting to see yet another name tribute in the family!
Incidentally, Joseph HYDE, Joel "Forbus" MOORE, and Stephen FINCH are all pensioned soldiers in the Revolutionary War.If you haven't done so already, you might want to view their pension documents.Ancestry.com has them (and some supplemental papers besides), but they require a paid membership.You might also try HeritageQuest.Some local libraries offer access (even from your home), as long as you have a valid library card.