Aside from what I normally buy I wait until they get here and take one or two to shop with me. Especially the ones with picky eaters. Last visit I got stuck with toaster waffles, applesauce, pretzels, yogurt, those fruit drinks plus other food and when I say stuck I mean a shitload of stuff. We don't eat any of that and no one took it home. They forgot. Lesson learned.
Since we live two minutes from 2 stores and numerous fast food places, waiting on the arrival was less stressful.
Another thing, my husband did smoked meats and BBQed, my sister and her boyfriend decided to eat Whataburger instead of eating our cooked food the whole time they were here. So that's another reason I wait until their arrival. Meat I can freeze but some things I can't. They all took home the desserts. They didn't forget that.
I don't mind paying for the food they want but I do mind wasting food. My pet peeve especially now with so many struggling to get food. I also bought a few of those styrofoam ice chests. Now there's no excuse.

For a group of unadventurous eaters:

Potatoes and fixings for a baked potato bar

Instant meals like soups, ramen, oatmeal cups

Bagels and cream cheese

Eggs

Bacon

Fruit and yogurt. For eating or for smoothies

Sandwich fixings

Snacks like chips, pretzels, popcorn

Cereal and milk

With three teens in the house, the food consumption rate will be extraordinary. Especially if the teens are boys. For lunch, I would have the aforementioned sandwich making ingredients on hand, but I would also arrange for lunch to be ordered in for at least 3-4 of those days. The teens can go pick it up! Since your in-laws are picky, I would err on the safe/boring side and do sub platters from Jersey mikes, order from local Mexican (assuming they will eat it), local pizza place, etc.

I hosted 7 adults, 2 teens and 1 toddler for TG. 5 days. We have one upright freezer so that was full of Costco appetizers and meals that we dressed it up.

Breakfast - 2 types of cereal, 3 types of milk, 2 types of toast, eggs, sausage, oatmeal, fruits, nuts and seeds, jam, butter, cream cheese, croissant, yogurt, granola, cheddar cheese, mushrooms, onions, tomatoes, spinach, avocado, tea, coffee and orange juice.

Lunch - I assemble and freeze - lasagna, burritos, curries, tomato soup. Also, I have chicken soup (Costco Deli Section), sandwich ingredients, salad ingredients, salsa, sour cream, shredded cheese, garlic bread etc. And I usually make some custard, cake and fruit dessert at least one day.

Dinner - Take out from Chinese, Thai, Mexican, Lebanese eateries. Ordered a fried 15 lbs turkey, made sides, got a a spiral ham from Aldis that needed to be heated and glazed. bought all pies from Costco.

I always ask what they like to eat for breakfast and lunch, and I press anyone who says “oh, anything is fine”. If I really can’t get info I go with cereal (cheerios is the standby in our family), yogurt, fruit, and bagels for breakfast. For lunch I do ham, a few types of cheese, lettuce and bread for sandwiches, ramen, and soup. I also make sure I have some chips, pretzels, and something sweet on hand for snacking.

Like other people have mentioned, but even more streamlined- I would lay out a continental breakfast(fruit, yogurt, toast/bagel) every morning with one hot item: bacon, french toast casserole, frittata. Lunch daily (if at home) would be the equivalent of a charcuterie board. Definitely find out about drink preferences. Some people can’t drink coffee without creamer, etc.

Op here, these are wonderful suggestions!! Thank you!