I just spent a few days with Mom, (89) and my stepfather of 45+ years. I had called him ahead and told him that I wanted the right to give my input to my mothers future care. He's hiding something. He's also lying about where their money came from. Patting himself on the back, while keeping money from my dad's veterans money that goes to mom. I judge from his conversation that he is trying to beat the system. Mom wants to stay in her home, and will finally accept some in home health care. They are in Nebraska and I in SD. Don't I have the right to know who drew up their papers and where they are? My stepbrother is executor. He lives in Denver. All my stepfather did to pacify me was to tell me about the hippa law, which I already know and had to fight for when she was hospitalized.
Do you have POA for your mother or does your step-dad or step-brother have that too? If so they sound like my step-mom and step sister in dealing with my dad.
Possibly the will just might be on file with the district clerk of court and the durable POA on file with the county register of deeds.
I'm afraid that without a durable POA, it's going to be hard to find these things. Most people do not put their wills in a safety deposit box. Rather they hide it like my mom did among their belongings just where you would never think to look.
You very well may need a third party to help address this problem. I wish you well.