Is it permissible to accept invitations from and visit and eat with and accept gifts from relatives and in-laws whose wealth is suspected of being unlawful?

There is no harm in accepting an invitation from relatives and eating their food, as long as it is not known that all their wealth is unlawful or that the food provided is unlawful. However, if that is known, then it is not permissible to eat, and they should be advised. There might be a benefit in not accepting the invitation.