I cook two dinners each night and the left overs are for snacking when they get home.

We have an air fryer and they make chips and chicken in it takes 19 mins

Cheerios dipped in tomato sauce.
Mini pizzas, You can get the mini pizza bases from the supermarket, and have the toppings ready to go.
We used to have them for dinner one night a week, on request.

Two options that are high in fibre and very filling are:
Canned baked beans, mashed, and spread on wholemeal toast.
Roasted chickpeas. They are in the gluten free part of the supermarket. There is a brand called The Happy Snack Company. Same company has Roasted Fava beans, but I have not tried them.

If one of them is keen on learning to cook, maybe on a weekend teach them to make savoury cheese scones.

The challenge is to guide them to snacks that are not junk food.

On the weekend bulk make bliss balls (even better, get them to do it) - can store them in the freezer.

Popcorn
Corn thins with peanut butter
Rice crackers
Corn chips with guacamole or salsa
Hommus with veggie sticks
Yoghurt with museli
Cereal
Toasted sandwiches
Smoothies
Fruit
Nuts: almonds, pistachio, cashews
Banana bread
Muffins
Pizzas made on English muffins
Crumpets
Pikelets
Scrolls
Milkshakes
Kabana & Cheese
Dip and biscuits
Sushi
Cookies
Creamed rice
Custard with fruit
Dried fruit

How about a tail mix you can put in a jar or big container so they can help themselves, just mix together whatever you think they'll eat: a range of nuts, sultanas or other dried fruits, pumpkin seeds, flaked coconut, puffed brown rice, puffed corn

My kids like to eat noodle cups and pasta packs, fruit, toasties, eggs, bacon, milo, nut bars, soup, pancakes, leftovers, yoghurt, chips, rice crackers, biscuits, prawn crackers, pies. They eat everything actually unless it involves putting more than 2 ingredients together 😆

Curried eggs: hard boiled, peeled, halved, then yolk scooped out and mixed with Keens curry powder and salad cream, then placed back in the whites. I used to do a dozen at a time, and they went very quickly.

I would cook bulk dinners, so there was always leftovers in the fridge for hungry hunters to dig into. Casseroles with vegetables incorporated in them are very good for that.

Rice Krispy Treats (LCM bars): you just melt some marshmallows and add in rice bubbles then let it cool in a lined dish.

Easy foccacia buns: equal parts plain full fat natural yoghurt, self raising flour, and any seasonings/add ins you like (I like to add herbs and cut olives, then top with cheese), mix it and chop into bits and bake. You could use greek yoghurt if you had that on hand instead of natural, as long as it's plain and is full fat.

I make my own pies and sausage rolls once a month to keep in the freezer, they're fully cooked you just microwave before eating, but that might be more than you're willing to do (its time consuming and fiddly).

You could make up burritos and freeze them.

Boiled eggs?

My best tip is: find a youtube channel of a large family and take their recipes. You'll get bulk amounts. But if your teens are anything like I was, they'll be happy to have the extra snacks available.