What is the optimal course of action if a brother prevents his sister from returning to her home out of greed for the father's possessions, with his intention being to evict the mother and two sisters after the father's death, given that the sister has no shelter or income?

The aforementioned brother has no religion and no morals, and he should not be obeyed regarding not returning. The emigration of a Muslim woman to lands of disbelief is not permissible except under very narrow circumstances, and residing in Islamic lands is far more preferable. With the distress, hardship, lack of shelter, and income, there is no justification for not hastening to return to prevent the brother's corruption. And Allah knows best.