Tex. Civil Practice and Remedies Code § 121.011

(a) The execution of an instrument may be established for recording by proof of the handwriting of persons who signed the instrument only if:

(1) the grantor of the instrument and all of the witnesses are dead;

(2) the grantor and all of the witnesses are not residents of this state;

(3) the residences of the grantor and the witnesses are unknown to the person seeking to prove the instrument and cannot be ascertained;

(4) the witnesses have become legally incompetent to testify; or

(5) the grantor of the instrument refuses to acknowledge the execution of the instrument and all of the witnesses are dead, not residents of this state, or legally incompetent or their places of residence are unknown.

(b) If the grantor or person who executed the instrument signed his name to the instrument, its execution must be proved by evidence of the handwriting of that person and at least one witness who signed the instrument. If the grantor or person who executed the instrument signed the instrument by making his mark, its execution must be proved by the handwriting of at least two of the witnesses who signed the instrument.

(c) Evidence taken for proof of handwriting must give the residence of the testifying witness. A testifying witness must have known the person whose handwriting is being proved and must be well acquainted with the handwriting in question and recognize it as genuine.

(d) Evidence offered for proof of handwriting must be given in writing by the deposition or affidavit of two or more disinterested persons. The evidence must satisfactorily prove to the officer each of the requirements provided by this section. The officer taking the proof must certify the witnesses' testimony. The officer must sign, officially seal, and attach this certificate to the instrument with the depositions or affidavits of the witnesses.