MINERAL RIGHT Lincoln Co. OKLAHOMA

I've been viewing comments and topics here and haven't seen a question like the one I have.

My late aunt had land in Lincoln Co. Oklahoma and each year a gas/oil drilling company renewed their lease with her. She passed away in the 80's and about a year ago we discovered that my dad (who died after she did) and I were in her will. We were told that because this land was part of the will, that my dad and I are entitled to a percentage.. The executor of the will, another relative, hasn't been cooperative and therefore we have no idea what to do. I do know that one can own land below the surface (mineral land?). Any assistance would be greatly appreciated.