I'm Doug, and I'm very sorry to hear of your situation. My goal is to provide you with excellent service today.
While you may have intended to rent the farmhouse to your son and family, if the rental agreement was never finalized, then neither your son nor any of his family have the legal right to be there. Your son's argument that he has squatter's rights is ludicrous and he is violating Texas law.
Quite simply, if your son has only been there for 24 hours, and he is there without your permission, he is not a squatter but is there illegally. The way to get him out is to call the police or sheriff and tell them that you are aware that he moved in yesterday illegally and that he has changed the locks and is denying you access to your property.
Once you have him out you can ask that the police charge him with trespass and ask them to issue a legal trespass warning such that if he comes back onto your property without permission you can call the police and he will be immediately arrested.
You may reply back to me using the Reply link and I will be happy to continue to assist you until I am able to address your concerns, to your satisfaction.
Please remember to rate my service to you so that I can be compensated for helping you. Thank you in advance.
I wish you and yours the best in 2015,