Perhaps do yourself a plate with just meat and vegetables for Easter lunch and tell your family you've had a bad tummy and want to eat simple food? I have the same issue with my in-laws, but after 6 months of severe allergic reactions last year (thankfully they've stopped) I've just told them that I'm still doing food elimination, so can't eat a very wide range of food, specifically no gluten, dairy or sugar.
But if you're really worried about not being able to resist, there is the option of removing yourself from the lunch altogether through sickness, but would you regret not spending the time with your family? It's a tough one...