California. My biological dad died without will, my stepmom and her children he had with her (I am firstborn) took everything, but am I owed anything?

So, my dad died a few years ago. I asked if he left anything for me or a will, and my hostile stepmother and hostile aunt yelled day me over the phone "No!" So, my stepmom and her 2 kids she had with my dad (I am firstborn) took everything... the house, the money, the boat, the vehicles, the vast tools, the artwork, jewelry, all the musical instruments... all of it. Now, she is trying to sell the house I helped build/rebuild/remodel as a minor that I lived in with them. I have sweat equity in that place. My dad died when I was an adult 6 years ago, but I didn't know what could be done about the situation. CAN anything be done? I feel she came in to deprive me of everything since my dad was a wealthy business owner with about $10 million in his possession at at least one point in time.