[Zeke]

Usually you pay for the car in front of you. You are responsible, right or wrong, to stop back far enough so this doesn't happen. That's not the real world, I know.

But, you shouldn't have to worry about any of this. Turn all the info into your ins co and let them do their job. If they decide no. 5 pays for all, then great. Either way, whether 4 or 5 pays your damages, you get paid. If you sue, you sue them all.