If my dad died, what rights does my stepmom have?

My dad recently died and we are not sure if he left a will. My dad was very protective of all of his things. His name was on everything. His wife's name was on nothing. He named his wife and me as having power of attorney on his living will and name me, my sister, and my stepmom as beneficiaries on his insurance policy. During his last weeks of battling cancer where he was not able to take care of himself, his insurance policy was changed (without our knowledge) to only include his wife as beneficiary. His house and other property he had was obtained years before he married her but she said she has rights to his house and land. I believe she was somehow able to change his insurance policy. And she's also removed over $7,000 from his bank account using his bank card after he died. Her name is not on that account. What recourse do my sister and I have?