Is it Legal for a Home Sale Without My Signature?

So, here’s the deal: My grandma recently passed away, and her house was supposed to be split between my mom and her brother. The thing is, her brother, who is managing everything, decided to put the house up for sale without even consulting my mom. Now, the closing is happening tomorrow and my mom is basically in the dark about everything. She hasn’t even signed off on the sale or the realtor’s commission. Can someone shed some light on this situation for me? Thanks a bunch!