debt collection on co-sign

[billaln]

What is the name of your state?Texas. My father-in-law, age 83 co-signed on a loan for a trailer home for his son. The son got divorced and let the trailer be repoed. He also co-signed for a cell phone for his grandson, the grandson used the phone in a towing business which he then sold and gave the phone to the buyer, who I would guess did not pay for it because the debt collector is now after Dad. They have also contacted him for balance of the trailer. The bill for the trailer is $14,000 and the cell phone $580.
I talked with our county attorny and he said to tell them to suck eggs as dad is debt proof. His only income is from Social Security and two pensions. He owns nothing but an 11 year old car with 125,000 miles. But I am worried that if they do sue they might get a judgement on the pensions, I know they cant touch the Social Security. He gets $900 from the USAF and another $100 from a private company. Are these pensions safe from garnishment?