also, walk where you can, eg, to the local shops, school, etc so just use your car for work and nothing else. Healthier too. I walk 3.5 miles to and from work saving myself £25 a week in bus fare (£100 a month) I also bulk buy things on offer and freeze them, things like staples (bread milk etc). I would buy mince, chicken, fish fingers etc in large quantities then you can defrost it in portions and make family meals as required. Get own brands of products like shampoo, washing up liquid and washing tablets, soap, bleach, sanitary towels etc. Cut your familys hair yourself. Buy clothes in end of season sale in the next size up (eg if you DC is 5 get them age 6/7 so they don't grow out of it quickly. Have showers instead of baths, or share the water for a bath, there is loads to be saved if you write it all down
I have 1000 after my bills and manage but there is only me to pay for as my adult children pay for themselves (2 at home aged 23 and 29) so its easier but I manage to live on 500 a month and save the rest for holidays etc but I know a family of 4 has a larger food and clothing bill but I do think you will manage. The main thing is for one of you to take control of the finances and budget accordingly
If your DH decides to go out for afterwork drinks every Friday or you get hair cuts and manicures that isn't budgeted for that's where problems start.
My parents cut costs when I was younger by writing everything down they spent, and I mean everything and then decided not to buy newspapers, to stop using the car for small trips, recycle items, eg cloths were washed and reused not thrown out. its actually quite enjoyable when you realise what you have saved.
Do either of you have expensive hobbies? I swapped to playing bridge as it only cost me a pound for a 4 hour night out and that included coffee and biscuits. Previously I spent a lot more out for a drink, meal or bingo. I still had treats and went out but by rewarding myself for being frugal when I needed to. Join Martin lewis money saving forum and look for vouchers, discounts etc online