Try adding small amounts of chorizo to things to give a good, strong meaty flavour. Patatas bravas, for instance, can be made into a delicious meal (according to my kids), but adding about 75-100gms of chorizo between 4 people. You can add it to pasta sauce in the same sort of amounts. bean and chorizo chilli is good as well. Just use a couple of tins of cheap kidney beans and about 100gms of chorizo instead of mince.
Cooking bacon can be used in potato bakes, pasta, soups etc. instead of more expensive rashers.
try eating more veggie meals. I know you say your family doesn't like lentils but have you tried things like dahl, lentil loaf or lentil soup? bean burgers are cheap and really easy to make. A favourite in here is pasta with caramelised onions. it's easy and really, really cheap, although you would have to get the gluten free pasta. Lemon pasta is a cheap, summery meal. Quiche is good too. Frittata can be eaten hot one evening and then cold in sandwiches the next day for lunch.
Oily fish meals - you could have kedgeree made with smoked mackerel. Fish pate made with tinned mackerel/sardines and soft cheese, pasta with smoked salmon trimmings, peas and cream. Mackerel with leeks over jacket potatoes is another cheap one with oily fish.
Cheap breakfasts might be porridge with a handful of raisins, eggs and toast or rolls and scrambled egg, toast and peanut butter with a banana, beans on toast.
Meal plan, what about:
toast and peanut butter, bananas
scrambled egg rice with peas
bean burgers, potatoes, carrot salad, sweetcorn
porridge
lentil and bacon soup, bread
pasta with smoked salmon, cream and peas
porridge
sandwiches with peanut butter and apple slices
patatas bravas, salad
scrambled egg rolls
left over lentil soup and bread
bean and chorizo chilli and rice
toast and peanut butter, banana
more left over soup and bread
frittata, salad
beans on toast
frittata sandwiches, apple
dahl and rice with chopped tomatoes and onions
porridge
crusty bread with mackerel pate
pea and ham soup (using the rest of the frozen peas and cooking bacon), bread, tinned rice pudding and peach slices
Spices - you should probably get garlic, chilli powder, cumin, curry powder/paste, chilli flakes