Texas Estates Code - EST § 1104.053. Guardian Designated by Will or Written Declaration

(a) Notwithstanding Section 1104.001 or 1104.051, the surviving parent of a minor may by will or written declaration appoint any eligible person to be guardian of the person of the parent's minor children after the parent dies or in the event of the parent's incapacity.

(b) After the surviving parent of a minor dies or if the court finds the surviving parent is an incapacitated person, the court shall appoint the person designated in the will or declaration to serve as guardian of the person of the parent's minor children in preference to another otherwise entitled to serve as guardian under this title, unless the court finds that the person designated to serve as guardian:

(c) On compliance with this title, an eligible person is also entitled to be appointed guardian of the minor children's estates after the surviving parent dies or in the event of the surviving parent's incapacity.