Is it considered a sin to withhold money from one's father if doing so would lead to the corruption of the marriage to the divorced daughter of the paternal aunt, and is it wrong to desire to marry her despite her being a previously married woman?

The right of a father is great, and honoring him is one of the greatest acts of drawing near to Allah. A father is permitted to take what he needs from his son's wealth, provided it is surplus to the son's needs. According to the Hanbalis, it is permissible even if the father is not in need, but it is not permissible to take if it causes injustice or harm to the son. Regarding marriage, there is no harm in marrying a previously married woman (thayyib) as long as she is religious, but the virgin (bikr) is originally preferred. If you wish to marry your maternal cousin, strive to convince your father, and seek help from wise individuals. If he insists on refusing with an acceptable justification, then leave her and seek a religious virgin; for obedience to parents takes precedence, unless there is significant harm in leaving her or fear of falling into what is forbidden. In that case, marriage without his consent is permissible, but you must continue to honor him and treat him kindly.