Legal Question in Civil Litigation in South Africa

There are a number of things that have to be looked at.

The house is presumably in the names of your deceased parents or one of them. There must be an executor to wind up their estates. He would deal with the house in terms of a Will or on the basis of intestacy. Then the house would become registered in the name of the beneficiary. You would have a claim against the estate for preserving the asset but you may have to pay rent for living in the house. Unless she is the sole beneficiary under the Will your sister does not own the house.