Monetary gifts / inheritences

My uncle died while we were married and my mom was the beneficiary for his life insurance policy. With that settlement, she gifted myself and my siblings $10k each. Can I get that back due to an inheritance or is that just a gift?

If you can trace the money back to the inheritance it is separate, if however that money was comingled and used for martial purchases, you cannot recover it.

It was deposited into our joint account and was spent along with all our other money. Is this a lost cause?

Yes, it is deemed to be a gift to the marriage.