If you want to do one of the Firework Dessert Parties - I would recommend the one at MK on the Tomorrowland Terrace. This will make keeping your party of nine together easier and in a non-crowded environment.
HOWEVER - your three folks with food restrictions will find limited options for them. There will be ways to avoid yeast pretty easily, but sugar? It's primarily a dessert party! There are some savory choices and I think they usually have a sweet or two made with artificial sweeteners instead of sugar, but their food choices will be more restricted.
In addition, the viewing is off-center. BUT - it you are looking for a way to escape the crowds and have a special experience - I think it will work for you. It is expensive.
I personally don't think any of the other special firework parties are worth it.
In general - if you are willing to sacrifice the TIME - you can stake out your spot for fireworks early - and have a runner planned to go get food - and if everyone is okay with waiting/sitting on the ground - you can still have a great time at fireworks without anything special planned. All of them will be crowded, with HEA the worst of those, but with the right attitude and patience, you don't need any of the add-ons to have a great firework experience.