Is it permissible to refrain from visiting one's parents, and how can one show them filial piety when they prefer their male children in treatment and finances, and mistreat their daughters and grandchildren?

It is obligatory for parents to treat their children justly, and it is not permissible to favor some over others except for a valid reason. However, this does not justify disobedience to parents or neglecting their rights, for their rights are great and are not forfeited no matter what their condition. Therefore, you must continuously honor your parents and treat them kindly, responding to ill-treatment with goodness. There is no objection to demanding justice from them and advising them gently and respectfully, or seeking the help of someone to advise them.