Has anyone on this thread got teenaged boys? The calorific requirements for teenaged boys are roughly double that of an adult woman. The OP is having to provide enough food for six of her.
OP - buy value pasta. Allow a bag per meal. It's about 30p a bag. Use a tin of tomatoes and some salt and pepper rather than a sauce, and instead of using quorn, use lentils and onions and make a bolognese.
If you are trying to save money as a vegetarian, quorn is not your mate. Lentils and pulses love you you, though.
Next, try to get a sack of farm potatoes, and wedge them. Serve them with carrots and peas and fried eggs. Still hungry? More potatoes.
Buy in flour, sugar and baking margarine. Want cake? Have fun, boys! Clean up after yourselves, please.
Four pints of milk a day? Not at all excessive IMHO. I get through that with me, an eleven year old and an eight year old. They both like milk - and milk, for your family, is a very important source of b vitamins.
Buy huge bags of brown rice. Boil it up, and cool it very quickly. Then you can use eggs, oil, peas and soy sauce to make egg fried rice. Super filling and tasty. Use brown because its more filling.
Buy cheap bread, not the fancy shapes. You would be surprised at the mark up per gram of bread once it's not a sliced loaf any more. Don't give the kids dinner money,provide a packet of ham and endless bread and let them make their own box up.
It is worth visiting supermarkets are seven, and buying up their reduced cheeses, fish, etc. freeze it. Use it when you need it.
Tinned sardines are a good source of oily fish, mix with left over mash and make fish cakes. Serve with whatever you have to hand!