I have a share in the house my sister is selling..dont I have a say in it before it sells

You indicated you had a "share" in the house.  Does that mean you are on the deed?  Or that you were supposed to get a portion of the house when he passed away?  If you are on the deed, then you definitely have a say in whether or not the house has to be sold.  If you were only to get a portion upon your father's death, then you will not have a say.  If your sister is selling the house to provide care for your father, then that is what has to be done.  If he had a stroke and needs care, and there are no more funds to provide care, then maybe your sister is selling the house to get the money.  She will be responsible for using the funds on his care.  If your father is coherent, ask him if he wants to sell the house.  Your sister should not be using the Power of Attorney if your father is coherent without his consent.