My Father has passed. I live in an estate house can I keep my sisters out and change the locks?

I' am not sure based on what you wrote if you already own 1/3 of the house, and will be inheriting more or all of the house.  If you already own 1/3 of the house, then you have a legal right to stay there.  If you are inheriting the house is an estate asset.  Technically you will owe rent to the estate, but you should have the right to buy out your sisters share of the house if any.  A lot is going to depend on what you own now, and what you will be inheriting.