Can property be sold without everyone signing off?

My sister (who is not executor of will), sold my dads home while he was still in nursing home with Alzheimer and without his knowledge. She sold it on a land contract. She did it behind everyones back so none of us knew. As far as I understand it, we all have to sign off before the house can be sold. She has done so many things, like threatening us of arrest if we do not sign. How can someone sell something that the will says, after his death, not before? How can she sell it if she is not the executor? How can she sell if the whole family has not signed off. This things stinks real bad. Thank you for addressing this issue for me