A partially observant relative passed away on Pesach, and I inherited him. I don’t know whether he sold his chametz. Is it permissible?
Chazal fined a person who possessed chametz on Pesach and declared it prohibited to benefit from even after Pesach (O.C. 448:3).
Some poskim maintain that the fine was not imposed on heirs when the owner passed away on Pesach, because chametz cannot be inherited on Pesach itself, so the heirs are not at fault to fine them afterward (Noda B’Yehuda O.C. #20 s.v. umei’atah).
However, most poskim maintain that the heirs were obligated to destroy the chametz on Pesach so that the fine applies also to them (Mekor Chayim 448:9; Avnei Miluim 92:5).
Nonetheless, when it is questionable whether the chametz was sold, there is a dispute among the Acharonim whether it is permissible to eat (Mishnah Berurah 449:5). Thus, if it is reasonable to think that the relative may have sold his chametz, it would not be prohibited — certainly where there is the additional factor of an heir.