Hi ElizabethB, some parts of this you can do yourself and some parts will require the help of an attorney. The county clerk property records for the Texas county should have some record of your ancestors mineral deeds and leases. Many of them are searchable online or through Texas file, although how far the records go back varies. If the property is still producing, the property tax rolls might also provide some clues. You will also need a copy of your ancestors will and will need to check that they did not bequeath the mineral rights to some other relative or a charity. A Texas oil and gas attorney can help you with the transfer of any mineral rights you might be in line for. Keep asking question here and good luck!