Oh it is depressing. I feel for you. 
But I also think that with your cupboard contents and some extra basics, you will be totally fine.
Porridge for breakfast. Porridge is under rated and is your friend. You could use half milk/half water - or the powdered as above, After all the ready made stuff is in powdered and that's ok.
Now, the way to do this is to soak it overnight, in the pan. One cup of oats for 2 cups of fluid. Your gang I'd do 3 cups of oats and see how it goes.
In the morning you turn your gas on, stir for about 3 mins, and the porridge is done. Super quick and filling for the adults and children.
Stick some sugar, jam, or the apples asRogerandPatricia say. You might have golden syrup lurking, mash a banana into it. Put drinkng choc or coccoa in the milk for chocolate porridge. Mix in the jam for strawberry porridge. Kids will love all that. Melt some marshmallows in for gloopy sweety porridge......look on it as a macflurry 
On the veg front, a bag of frozen peas and some frozen sweetcorn will serve you well. Sling some in pasta, big blob cheap mayo and a tin of tuna and you have jacket potato filling. Some black pepper will cheer it up.
If you aim to eat veggie for 5 nights I almost promise you the money will last easily.
Go for root veg. Roast parsnips, sweet potato, squash, all these are filing and give yo a large lump of nosh for the money. You can turn them into mash too.
3 tins of toms, chopped onion, glug of oil = pasta sauce. Use whatever herbs you have to hand, or none if there are none to hand.
drinks - buy own brand carton of litre of orange juice, and water it down. Tastes ok, bit like squash but nicer, and I can get 2 litres for 58p.
HIt is crappy though. The only thing you can do is look on it as a challenge, a 'lets prove we can do this' and maybe even keep going or do it agan in a little while. Save the money you save for a treat for the family