Is the money my friend took from the girl's mother lawful or unlawful, knowing that her father works in both lawful and unlawful projects, and that the money is in exchange for the girl dropping her right against him?

As for the daughter waiving her right and absolving the father of the remaining money, his debt has been cleared, because a debt is relinquished by absolution, and what has been relinquished does not return. As for the money he took from the mother, it is a settlement that he is not permitted to take, and he must return it and cease his harm against the daughter and her family.