I'm sorry. I know it is supposed to be polite and the right thing to do, but I grew up having to eat everything from my plate, whether I liked it or not. I will never, ever make anyone eat anything they do not like just to be polite. I also have Chronic Acid Reflux and not the world's best gag reflex. So, in order to be polite, I should eat something I am offered whether I like it or not, but, which is better. To be polite or vomit everywhere?
I think you, the daughter, not your dh, need to tell dad that he should not buy a boat load of shrimp. Let him know one child and your dh do not like shrmip, so they will not be having any. Dad, we want to save you spending money you don't need to, so just buy enough shrimp for son and me. I would also bring or buy plenty of extras, like corn on the cob, baked potatoes, etc., so you can fill up on that and I would be hiding my uneaten shrimp in a napkin as discreetly as possible so dad does not notice.
If dad sulks, so be it. You state there is no winning, so why bother trying? Time as a family to stop enabling him. Instead, if he does not eat with you, make sure that you have a really enjoyable eating experience. Laugh, tell jokes, stories, etc. Make it such a good time that dad eventually joins you on his own.
Like others have stated, go out to eat. Come back laughing, all happy each and every time. Talk about the great food you had. Gee, dad, we are sorry that you missed it. We would have so loved to have you with us. Maybe next time. (Not to rub it in your dad's face, but in a way that shows that you would really have loved him to be there, or in his house, for him to be included in the festivities, whatever they may be).
Or like it is always stated, You cannot change others, but you can change how you react to others and how you deal with certain situations.
