You will need a court order to compel them to release the information and then the money. You will have to file a lawsuit seeking the equity in the house from them and, as part of that, you will be able to use the legal process or procedures of "discovery" to get the information you need. At the end of the suit, the court can order them to pay whatever amount, less costs of sale and paying off the loan, you are entitled to. If the estate has not been fully probated, the personal representative or administrator should bring the suit on behalf of the estate; if it has been probated, the heir(s) can bring it.