Is it unlawful to file a lawsuit against a father for not spending on his children and for failing in his duties, while being financially capable?

It is not permissible to sue the father, for that involves disobedient conduct (ʿuqūq), which is forbidden. However, it is permissible to advise him with wisdom and good counsel. Indeed, it is among the gravest sins for a person to neglect those he is responsible to provide for. If the father is remiss in his duty towards his children, this does not negate his right to dutifulness (birr), nor does it permit them to treat him badly or deal with him harshly and cruelly. Furthermore, equipping the daughter and helping her with marriage is not obligatory upon him, unless he was the one who received her dowry.