Gwen - where did they get the alcohol? Your ex may be opening a can of worms for his own daughter if she was party to obtaining the alcohol. Its not just who was driving the car its where the alcohol came from in these cases with minors. For example if you allow teens to have a party and provide them with alcohol then you are the one sued not the insurance company. If minors buy liquor from a store then its the store that is responsible. If the girls stole the liquor then they are both responsible. If your daughter is the one that obtained the alcohol then he himself could be liable as her parent. i'm sure your daughters medical bills can be paid from insurance but since they were both minors and she was a willing party to the whole thing its going to be pretty hard to get anything else.
I'm in the legal profession and there are always those people who no matter what happens look for the edge to get something. there is also the case that with the medical bills and car damage there may not be much left over for his pocketbook and in that case the money comes from the parents so he is suing them. I really dont think he is going to be able to get much - especially if you are standing by saying this is both of their faults and not just the other girl. Without you on his side in the lawsuit he'll have an even more difficult fight.
these litigious people really bother me - they are what causes all of our insurance to be so expensive and medical bills to be so high (becasue of malpractice). I did personal injury law for a while and just didnt sleep well at night becuase of all the scams so now i do real estate - i just sleep better knowing i'm not helping scammers. I just hope his attorney isnt an ambulance chaser and will set him straight. If he does get some money it better go into a trust for your daughter.