A yeshiva bochur asked Rav Chaim Kanievsky about a difficult predicament in which he finds himself. He tells Rav Kanievsky that he, as a yeshiva bochur, keeps the Torah and mitzvos like all yeshiva bochurim, but unfortunately his family does not. At all. In any way. They respect his choice ot be frum and learn in yeshiva, and he respects them and their lifestyle, but he wants to go home and stay there for Pesach. He says that while they would be eating actual chametz on Pesach, he would have his own shmura matza and wine and everything else needed for a pesach sedder, but they refuse to clean the house from chametz and to stop eating the chametz. He says his mother told him that he can eat whatever he wants, whenever he wants, however he wants, but he should not bother them.

The young man asks Rav Kanievsky that if he stays home, they might eat matza with him and eat with him at the seder, but is he allowed to stay home considering the halacha that one cannot live in a place with real chametz present lest he come to eat from it himself. However, if he goes away, they'll eat the chametz as well, but he himself won't feel as a free person.

Rav Kanievsky's response was that he should do whatever possible to find another place to sleep and eat during Pesach and not go home where they will be eating real chametz. Rav Kanievsky added, surely you will find an appropriate place as everyone says at the seder "kol dichfin yeisi vyeichol" - let all who need come and eat.

Rav Kanievsky added that while he has heard that some people sell the chametz belonging to non-religious relatives, using the din of "zachin" - doing something good on behalf of someone else even without his knowledge works because it is presumed he would have wanted it, it definitely does not work if they are continuing to eat the chametz that was "sold" as they are then showing clearly they did not want the chametz to be sold.
sources: Kikar, Kol Hai News, Behadrei