Don't sign boilerplate settlement agreements that say that you're releasing "everyone" if you want to preserve your right to sue someone else. Even if it's boilerplate, even if there was no real intent to release everyone by any of the parties, and even if the insurance company who prepared the boilerplate agreement admits that it's a standard form and they didn't give a whit about releasing anyone except the insured, the trial court will hold that the release means what it says.
And the Court of Appeal will affirm.