All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Doing innovations by your family has no influence on the legitimacy of their food; i.e., it is permissible to eat their food. But, if they slaughter an animal for the sake of some grave or its occupant, or they mention any other name except the Name of Allah while slaughtering, then it is unlawful to eat from such a slaughtered animal.
In addition, if anyone of your family believes that such an occupant of a grave or any Wali (a faithful obedient servant) can do what he likes in this universe (i.e. good or bad for people) or seeks his help, then such a person commits Shirk with Allah. So, such a person's sacrifice becomes unlawful.
Moreover, it is better to live with them so that you can help them avoid any innovation. Here, you have to advise them politely, kindly and with wisdom.
Also, you have to show patience while dealing with them so that they may return to the right path at your hand, and everything is in the Hands of Allah.
Allah knows best.