Hi 6438karl,
Was there a will. If there was, then there would have been an executor who is responsible for carrying out the wishes of the dead person. It is up to the executor to obtain a valuation of the property, normally from one or two estate agents, and sell the house accordingly.
Under normal circumstances, once a valuation has been agreed by all parties it is up to them to come to an agreeable arrangement. The other person involved would by law have to buy your share of the property. If this couldn't be done for one reason or another then it would be up to the executor to use his power and exert his authority.
Regards