What should someone do who has amassed a vast fortune from unlawful money and wishes to purify his wealth after marriage and having two daughters, fearing for them from the unlawful?

You must repent to Allah. Money taken unjustly must be returned to its rightful owners as a condition for repentance. As for money acquired from unlawful work with the consent of the other party, it should not be returned to its owners; rather, it should be disposed of by spending it on the welfare of Muslims. You are permitted to take from it what suffices you for a permissible livelihood.