Texas law will, of course, determine what the proper answer is. I do not know if a Texas attorney is available to give you a specific and better response than I can.
I would hope that Texas law would provide a specific remedy, such as giving them written notice that, if the materials are not picked up within a specified time that they will be deemed abandoned and can be disposed of by you. Unless a Texas attorney provides a better response, I recommend that you do two things:
1. Take some good photographs of the items left behind, and ask friends or neighbors to view the materials and make a memorandum of what the items are and their condition and (if possible) even their estimated value. This is to protect you in the event you do dispose of the items at a future date (even in compliance with Texas law) and your former friends accuse you of disposing of valuable assets without justification.
2. Confer with a good real estate lawyer in your area. The information that you can get from such a conference will be well worth a modest conference fee.
Answered on Aug 18th, 2012 at 3:23 PM