Is it obligatory for us to maintain ties with our maternal uncle who wronged us, insulted us, and stole our father's money, given our father's complete objection to our maintaining ties with him?

Your reconciliation with your maternal uncle is a good deed for which you will be rewarded, because maintaining kinship ties is an obligation.

You should strive to convince your father to allow you to maintain ties with your maternal uncle and remind him of the seriousness of estrangement, seeking help from someone who holds influence with him. Strive to reconcile them.

If your father does not agree, then it is not permissible to obey him in severing ties with your maternal uncle, for there is no obedience to a creature in disobedience to the Creator. Try to maintain ties with your maternal uncle without your father's knowledge, if possible.