Is helping the mother considered disobedience to the father? And what is the ruling on shunning a father who demands that his children not visit him, claiming they cause problems with his wife? And in this situation, does obedience to the father take precedence?

Orphanhood only applies before puberty. Caring for the mother and providing her with means of livelihood is an obligation upon her daughters, even if it displeases the father; for there is no obedience to a creature in disobedience to the Creator. The father's cutting ties with his daughters due to their misconduct does not permit retaliation in kind. If the father claims that their visits cause him problems, there is no harm in temporarily suspending visits while continuing to check on his well-being and maintaining ties with him financially or otherwise.