My question involves estate proceedings in the state of: Tenn

Hello we live in FL my in laws are from Tn.My father in law passed away.My Husbands siblings showed
up on the doorstep of his house with their hands out one getting pretty nasty the day after he was buried.My husband and I were very upset to find this out.We expected it all to go to my mother in law (step mother to my husband
and his brother and sister) and when she passes some day any assets and family heirlooms from
prior marriage to be divided between my husband his sibs and the one step son from her prior marriage.
There was a will from a insurance each his kids get 1,000.00 my husband didn't even
want that because he was worried how she will make it.She told us she wanted no more to do with the
brother and sister.they each had to sign a letter before they got the check.
the check came here with the letter stating we agree we have no further claims to the estate we are
now confused.We don't want to cause a problem for our mom as we think of her.But I also want to protect
my husband when she passes.They were together 17 yrs.They both worked together for all they had so
we feel its just as much hers.But she's not in good health herself every one was shocked he died first
but he got cancer.If we sign the letter is he saying he has no claim to his family possessions like his fathers
Flag family photos videos from his first marrage.and share in the estate.We think they are planning on selling the house
again we don't care if its to get her a place.but once she passes to ?