Tell your ins co to offer the full limits of your policy to anyone making claims against you and to get releases. Otherwise they have to defend you. You are jointly and severally liable for economic damages, and only liable for your share of the general damages.
The nonuse of the seatbelt has important bearing on damages but there are many other considerations. I presume that you have substantial fault, as in my experience that many cars piling up in front of you before you joined the melee indicates that you were probably following too close.
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