I quite frequently cook for mixed groups of veggies/die hard meat eaters and find the key is either meals where the sides are the same for both and only the 'main' element needs substituting, or where the veggie main element is pretty substantial and then some meat can be added almost as an afterthought...
I'd do baked camemberts for everyone one night, gorgeous studded with rosemary and garlic, with crispy bread for dipping. With a salad and perhaps some vegetables on the side I'd say that's substantial enough for a light dinner, but if you have some who really 'need' meat with every meal, they could have some charcuterie or gently warmed chorizo/sausisson on the side... If younger children don't like the taste of the camambert (although it's milder cooked) they could have some melted milder cheese as a kind of fondue?
Then I'd do a big barbecue another night, whatever meat the meat eaters like and for the veggies they could have veggie/cheese skewers (larger supermarkets will sell halloumi or sub with any firm cheese what won't melt over everything), or large grilled flat mushrooms to make into a 'burger', or you may be able to find some halloumi or falafel for them in a larger supermarket. Or if you are up for a bit more effort, for easy bean burgers just mash up some tinned beans with chopped onion, bit of cheese, seasonings and an egg - they'll likely be too sloppy to cook on the BBQ but just fry them in a normal pan with a little oil. Same sides for all - bread/spuds/salads/dips/corn on the cob.
If you need a 3rd night, I would do something for the meat eaters which is served with potatos and veg, so a french stew (coq au vin or beef carbonade are nice) or roast chicken (you may need 2!) and chips or similar, and the veggies can have an roast stuffed pepper, something along these lines...
www.bbcgoodfood.com/recipes/4404/easy-stuffed-peppers
I always do at least a few 'picnic' suppers in France (especially if we've eaten out at lunch) - bread, charcuterie, selection of cheeses, olives, crisps, dips, lovely fresh salad, red wine etc. With fresh patisserie for afters! Veggies can just pick the veggie friendly bits from this. Anyone who feels this is insufficiently substantial could whip themselves up a quick omelette or cook some sausages to go with?
I do hope you are eating out for some meals or can do some easier cold meals as above, cooking (and then washing up!) for 11 on holiday could get quite old quite quickly even alternating nights - and I say that as someone who likes cooking!