(a) To exercise its option to purchase, the tribe must file with the agency:

(1) A written notice of purchase; and

(2) A certification that the tribe has mailed copies of the notice on the same date to the judge and to the affected heirs or devisees.

(b) A tribe may purchase all or part of the available interests specified in the probate decision. A tribe may not, however, claim an interest less than decedent's total interest in any one individual tract.