My question involves a consumer law issue in the State of: Texas

My son-in-law got one of them stupid title loans on his truck a couple months ago, well the other night he got in his truck to go to the store and before he even put the key in the ignition, all of a sudden his truck starts moving backwards out of the driveway. Well, he looks in his rearview mirror and sees the reason for the truck moving is a tow truck. So, he steps on the brakes and starts the truck to let the driver know he was in it, which the driver then starts raising the truck higher causing it to fall on it's side, which totals my son-in-laws truck. The police wound up getting called and when they get out there, they tell my son-in-law that they can take him to jail because he was illegally in his truck because the truck did not belong to him it belong to the title loan place. Well, my SIL called the title loan place yesterday to tell them what happened & they told him that the tow truck driver is supposed to get out his vehicle and walk around the vehicle being repo'd to make sure there is nobody in the vehicle and that the doors and steering wheel are locked. Which of course, that didn't happen, otherwise my SIL wouldn't have been in the vehicle and been injured when vehicle fell over while falling off the tow truck. Truck was never taken out of park during all this.
How is it illegal for him to be in his vehicle, in his driveway fixing to go to the store and a tow truck back up into his driveway and hook his car and then start to drive off without even securing the vehicle? Who is liable for the damages and injuries sustained? I would think that since the police released vehicle to the tow company and the vehicle is pretty much totaled, my SIL's loan is now paid because of the repo. They are thinking about suing both the loan place & the tow company. When they go the tow company, does anyone have any advice on questions they should ask or anything they should look for and same for the title loan place that could help them make a case if they do decide to sue?