@Icannotbudget Loads of helpful replies on here! Trying to add some tips to the mix too. I also have 2 teen DS and they descend like locusts as soon as I do a shop, and moan on about getting enough protein, so I've had to get creative with filling protein-based food, too. [Edited to add - I'm also a single parent and work a very intense FT job, but I do the cooking at weekends or evening. Can't deny it's a ball ache sometimes!].
I've had to ban cereals as the price is extortionate, same with yoghurts and any dinky snacks as they are just overpriced. Breakfasts are porridge (cheap) or a tortilla omelette (cheap tortillas, mix up eggs (cheap), grated cheese (cheap) and chopped frozen peppers and onion (cheap). I also make protein egg muffins (omelette mix in a muffin pan, take on the go, plus a banana - filling and cheap).
I also second Costco if you can get membership, the fruit and veg is really good quality and tomatoes/bananas for example significantly cheaper.
If I need to do the meaty protein that is always demanded, I bulk it out and often do a cheap French dish with puy lentils (green), cooked in onion, garlic and stock, AND chopped potatoes and carrots (so really filling) and I'll add just two smoked sausages that gives flavour and the 'meat'. Costco does big packs of Italian sausages so this works out well.
I also do tray bakes of chicken thighs with frozen peppers (cheap), and potatoes (cheap) and I'll stir through a load of quinoa too (protein and cheap), so again its really filling, and there's leftovers for school lunch.
These may be relevant to your non ND son or husband.
Are there any markets near you? Household market stalls are good for £1 deals on cleaning products, bleach, bin bags, deodorants, cheap snacks etc. I also do markets at the end of the day when they are doing deals on big bowls of fruit, bananas etc. Poundland also has all the basics are cheaper prices, and I've also made my own cleaning products with baking soda etc. Waitrose own brand and packs of 3 for £10 are better value and quality than elsewhere.
I manage to keep costs down, but I do trek about to different places.
AND your DH needs to step up.