You know what? I'm going to host a family dinner and serve a dish that has peanuts so that my sister and her kids can't attend.
Oh my goodness, you can't be saying that for real. Why would you serve a dish that your sister and her kids can't eat?
Because my sister and her kids exclude me from activities all the time.
I'm sure you must be frustrated with your sister for her actions but purposely excluding them from the dinner is wrong. Talk with your sister about how you feel and try to understand what the issues are between you. You shouldn't make something to share that others cannot eat because of their dietary restrictions.
I really want to hurt them for leaving me out.
You have to understand life is sometimes not fair. Why not just talk to them or joke about how they always exclude you and you don't do that to them? This is a better idea than excluding them out of spite or making a dish with peanuts so they can't eat it.