I think go with something that can be made in advance. Have they said what the issue is with your suggestions?
Sausage casserole and mash (basically sausage, mash and onion gravy but simpler as you do sausages and gravy together)
Chicken fajitas - make a load of lightly spiced chicken, salad, grated cheese, salsa etc and people can add what they like.
Pulled pork, Rolls and salad. Sweet potato fries if you need extra carbs.
chicken and chorizo pasta. I get those little bits of chorizo, fry with chicken and add onion, garlic. Add smoked paprika, tinned toms and cream cheese. Stir through pasta and serve with grated Parmesan and salad.
Buy a few nice ready made curry or Chinese dishes from M&S or Waitrose plus sides (or a couple of those big mixed boxes).
chicken tikka masala in the slow cooker with rice, some supermarket bhajis and samosas and naan.
bung some chopped chicken in the slow cooker with some supermarket Chinese type sauce - black bean or similar, cook for a few hours, add veg 15 mins from the end and serve with rice or noodles, bought spring rolls and prawn crackers.