Ross, haven't been on here for a week ('puter probs). This is a real mess. I'm so sorry for you and Lyn and your son and his fiancee and her mom.
Your son really needs a lawyer. He should be able to get one on a contingency basis since there'll be a lawsuit. If he wasn't driving the car, he might be covered by the liability coverage on the car, as well as uninsured motorists because he isn't related to the owners of the vehicle. I wish I had a copy of an Ohio auto policy (no longer within my grasp since retirement). Ohio has some really weird auto insurance laws, as I recall - pretty consumer-friendly. So it's imperative that Chris gets a good insurance lawyer and not depend on one that covers the car he was in. He probably won't like the idea that there's going to be an adversarial relationship between him and his fiancee's insurer; but he needs to suck it up and get mercenary real fast.
Anyway - all my prayers to you and Lyn. I'm sure a lot of your son's snottiness is the result of the accident - PTSD, pain, fear, dependence - and things will begin to look up.