By virtue of WILL, property already had become self acquired property of your husband (1/4th) after his father`s death. So status of ancestral never acquired. And partition is not valid as effects between joint owners and MIL was already disinherited by WILL. It should have been settlement or GIFT deed. so , MIL settlement deed also without ownership and void. MIL can have share from deceased son 1/4th.
Adopted child has no coparcerny right. Set side partition shall be filed by husband.
Release deed executed by paying money, no chance of revocation.