I'm with DB on this one. Have your own celebration and leave them to their dyfunctional mess. EveningRose's "scapegoat" theory seems right on here--don't get "guilted" into buying into the drama.
I suggest you be polite, distant, but absolutely firm in declining any family functions you don't want to join in. They will get used to it over time and maybe they will see the problems are still there, with or without you.
Most importantly, their opinions are not facts. Don't internalize their BS. You are a good and loving person and don't let their meaness get to your heart.