In general

(1) if both parties carries out the agreement by themselves and carry out the agreement, then there is no need to bother the US court.  They just sell the house, split the money, there is no need for legal assistance. 

(2) if one party refuse to carry out the agreement, one party has to sue the other party in the locality where the property is located.  The fact they have Texas driver license is not relevant.  The key is where the property is located.  Find a lawyer for that locality.