What is the ruling regarding gold jewelry gifted by a man to his two wives and used by them during his lifetime: does it become part of the estate after his death, or is it their private property?

If the husband gifted jewelry to his two wives during his lifetime, and they took possession of it by using it, then it belongs to them. The general principle is that jewelry in the possession of women is considered their property, unless there is evidence to the contrary. If it is not known whether it was a gift or a loan, then one should refer to the prevailing custom in the community. If the custom dictates that they own it, then it belongs to them. If the custom dictates that it remains the husband's property, then it is considered part of the inheritance and is divided among the heirs. "Custom is a ruling authority" based on Allah's saying: "And give them their due compensation with fairness" (Quran 4:24), and the Prophet's (PBUH) saying: "Take from his property what suffices you and your child with fairness." It is preferable to refer to the Sharia court because it is more knowledgeable about local customs.