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You need to find out the liability limits of his policy. The potential problem is that his policy limit may not be high enough to cover the damages to all 3 cars if he has the minimum coverage. Then your uninsured/underinsured coverage will have to kick in and cover the rest. Your insurance company will likely file a suit against the driver personally if he is found to be negligent and there are significant damages in excess of his policy limits.
You don't need a lawyer. Your insurance company handles that. Glad you are alright and best of luck.
Graham, why don't you give us a professional's advice on it?
...as was already mentioned by Black Betty...he's always offering to help with insurance issues (his profession, I believe) and he's currently listed as an active user as we speak. Good luck moving forward.