Disowning Family Members

My grandfather was an evil genius.
When he passed, it had the it set up so that:
1. Nothing could be sold as long as my uncle and dad were still alive. They were to collect rent from the property so that they both had some sort of income. (My grandpa lived thru the depression, so he knew absolute poverty).
2. After the two of them die, it would take all 7 of the grand kids to agree on the sale.
Here's where the problem comes in. My uncle passed away before grandpa in a car accident. That left only dad. I have two cousins, a half sister and myself and three siblings.
One of my cousins died of cancer shortly after grandpa died. The other is in prison in California. He's a three striker. He's 7 years into 25 to life. The problem is my half sister. She's decided that since she's a half sister, she deserves 1/2 and me and my siblings get the other half. Not 20%, but 50%. Her argument is that dad left our mother because she was obviously horrible and her mother was the better option. I'm convinced that this is equal parts her and her idiot husbands idea.
Aside from the fact that is a stupid argument, she tends to forget that my dad has been married 8 times. Since he's not dead yet, I won't be surprised if there is a #9 or even #10.
So.......
When dad dies, I and my siblings refuse to agree to our 1/2 sisters plan and I guess we're going into the landlord business.