ما هو الحل الشرعي الإسلامي للتعامل مع أب انحرف عن الطريق المستقيم وأصبح يخسر أمواله في الحرام، ويرفض النصح؟

Striving to guide one's father is one of the religious obligations and a form of showing him righteousness. One must strive for this with gentleness and wisdom, and employ all possible means to encourage him to commit to acts of obedience. You can seek help from those who influence him, or discuss the matter in front of him in a way that does not hurt his feelings, or play for him audio recordings of scholars whom he trusts. It is also good to invite some righteous people for iftar (breaking fast) so they can get to know him and assist you in his matter, for "A man is upon the religion of his close friend." Most importantly, your kindness and righteousness towards him will help you gain his trust.