You could add a “Custom Group Type -> Exclude” as a custom group for you item and exclude all ingredients as required
for your normal and large sizes.
Personally though I would think it would be much more elegant if you were to simply have 2 menu items
a) Pizza Party – > with Add Ingredients enabled
b) Pizza normal , family -> without Add Ingredients enabled
would make it a lot easier to maintain in the long run too I would think, but that’s entirely up to you of course