Now that you’ve been summoned, do not discuss the case/accident with anyone. As a former cop, I can tell you that anything you say about the situation could come back to haunt you. I agree with the others, UPS is the target, not you. The lawyers go for deep pockets, even if you’re a recent lottery winner UPS still has deeper pockets.
If your manager is a good one, he’ll make sure you have zero contact with the plaintiffs as their delivery driver.
If you’ve been summoned to give a deposition, be honest. If you don’t know the answer say you don’t know. If the case goes to trial, the answers you gave in the deposition are expected to be the same at trial. Anything different could lead to perjury charges. Think I’m kidding? It happens every day.