Generally in a rear-ender the person who started it is at fault. I was also in a 4-car collision like this in January, unfortunately, my car was the first one hit, so the car took it in the rear & front. Car ended up being totalled.
I never heard from anybody else's insurance company, I assumed our insurance companies all went after the at-fault driver's insurance. Just one suggestion for you to watch out for, since there are 4 cars involved, make sure you stay on top of getting your car fixed and filing any forms you need to take care of any other property damage. Just in case the at-fault driver's limits runs out, you want to make sure you get your claim in the pipeline early.