Intestate Laws and Rights of Biological Children/Stepchildren/Adopted Children

In California, My dad died intestate 2015, my stepmom died suddenly December 2019 (doctors were puzzled) intestate. No probate has been filed on either. My stepmom had a son that was legally adopted when he was young. My stepmom gifted her son/made him beneficiary of my dad's IRA. I don't even know if she was beneficiary to my dad's IRA, she took over my dad's accounts/my grandfather' that my dad inherited accounts, she attempted to get my brothers and my life insurance policys taken away. What can we do? My Dads house was separate property however, I guess she gained a 1/3 through intestate succession. Can her son get the house too? She was never designated as executor of anything. What do My brother and I do? Turns out she also gifted her son a house she inherited from her parents. I believe my dad had a handwritten will. Don't know what to do??!