How do I fight for my Father's properties without him having a will?

My Father passed away without a will very suddenly. My step mother passed 8 months later from lung and brain cancer. My step sister is executor of the estates, but I think my parents were not legally married from some paperwork we found after their deaths. My step sister is no longer speaking to me, and I want to ensure my biological sister and myself get what is rightfully ours. My Father owned thousands of dollars worth of firearms, which are in the possession of my step sister's husband. There is a lot of property and a house in both parent's names, and at the time of deaths, over $30,000 in a joint bank account. I need to know my legal rights.