It is possible to feed a family a nutritious, balanced diet on less money, but it takes work and planning.
I'm a SAHM to a 5yo and 2yo, we also have my brother living with me, so 3 adults and 2 young kids. We have pets, both kids wear nappies at night. I'm gluten free, one child and two other adults are dairy free, so we have to buy alternatives. We don't eat a lot of meat, one adult is vegan, but we do tend to have chicken once or twice a week, sometimes a roast.
Our weekly spend, including dog food and all household cleaning stuff, nappies, laundry etc, hovers between £90-£100/week. My brother will pop out for the odd thing separately and we occasionally do a little top up bringing it to the £100 mark, but it's definitely not up to the £140 mark, and I feed us all a homecooked meal every night.
We eat really well! Always get our 5 a day (we spend a lot on fruit as snacks) and I really pride myself on making sure the kids have plenty of protein and veg. We don't do a lot of freezer food or filler carbs, no ready meals etc. Both kids and I eat lunch at home together daily, husband takes a packed lunch. It takes so much work and planning, but I see it as part of my role within the household as I have the time to do it around parenting.
It is possible, if somebody cares enough to put the time and effort in. Unfortunately it doesn't sound like your husband does. But he should, as it would make a huge difference to your bank balance, your enjoyment of food, and your family's health. I'm not trying to be preachy in any way and I am totally on your side. It just doesn't sound as if there's any good reason why he can't inform himself better and try harder.
In case this is helpful, this is my meal plan for dinners this week:
Tues: rocket & pea pesto spaghetti with butter beans and/or mackerel, cucumber salad on the side
Weds: chicken, apricot and chickpea tagine with couscous/rice
Thurs: sausage, root veg and mushroom casserole with garlic bread
Fri: veggie stir fry with rice noodles and satay sauce
Sat: lentil & veggie mince Shepherds pie, sweet potato mash on top
Sun: chinese style baked Cauliflower with orange & sesame sauce, egg fried rice
Mon: mushroom & spinach risotto
Breakfasts are usually porridge, muesli or granola with yoghurt, eggs, toast
Husband takes leftovers or wraps for lunches with salad, chickpeas, tuna etc. Kids and I will have soups, omelette, quesadillas, sandwiches, usually with fruit and yogurt.