Is the questioner sinful for remaining in a house where there are unfulfilled rights of heirs, knowing that his father postponed the payment of these rights?

Your father is not permitted to monopolize the inheritance to the exclusion of his sisters. He must return their share or purchase it from them, and hasten to clear his conscience before it is too late. You must advise him and remind him of the gravity of consuming the wealth of relatives and severing kinship ties. Seek the help of righteous people to remind him of the severe warnings against injustice in inheritance, such as the hadith: "Whoever usurps a handspan of land unjustly, Allah will encircle him with it on the Day of Resurrection from seven earths." As for the usurped house, it is not permissible to remain in it, and one must leave it. Prayer in it is a matter of scholarly disagreement; some, like the Hanbalis, deem it invalid, while others, like the majority, consider it valid but sinful, because prayer in a usurped place is forbidden, so how can one worship Allah by disobeying Him?