AITA for forcing my younger sister to sell our family home after our mom died

So. My mother died last Wednesday. She wrote on the will that the house belongs to Sister1 and if she sells it, 90% of the proceeds go to Sister1 and 10% go to me. Problem.

There's a third child, an estranged sister. Lets call her Sister2. And my mother did not get the will witnessed or notarized which in Florida is needed to uphold a will.

Sister1 has been living in this house for about 10 years now. But every lawyer we've talked to has said that it doesn't matter the house will be split three ways by a judge.

Sister1 wants to keep the house, even though she can't afford the mortgage. And technically she can't even keep it since it belongs to all 3 of us. She's saying I'm an asshole because I'm not giving up my third of the house to her like our mom wanted. AND for not helping her pay the mortgage she can't afford. She's refusing to start any of the process needed to put the house under the three siblings names and sell it. So we can try to sell it.

If we don't sell it, and she misses any of the mortgage payments the house could be lost and then no one gets anything. I offered to help with the mortgage for 6 months to hopefully sell the house in that time. But she's still saying I'm not doing enough to help her keep the house and should be helping for longer while she continues to drag her feet and prolonged having to split the house three ways.

Next week I'm going to go above her and start the process myself since technically any of the three of us can do it. She hasn't even told Sister2 that she has a claim to the house. She's been trying to find loopholes to cut her off since she was estranged from us. But sorry. Legally she has a right to a third of the house. She also wants us to buy her out, but I don't have that kind of money and I have no problem with the house being split.

I dont understand why I should be expected to give up my legal right to a third, and help her pay the mortgage.