Oklahoma Oil Trust Fund

Oklahoma

Dear Sir or Madame:
My grandfather passed away and left an oil & gas trust to my mother, siblings, & me. It is split up in the following way:
Mother: Received half of the whole
Grandchildren: Received the remaining half which was then divided into equal parts among the grandchildren.
My question is this: Are the individual grandchildren aloud to borrow against the trust to buy a house and is there any way of finding out how much the trust is worth in total?
I would appreciate any information you may have.