For me, income, mortgage, council tax, insurance, etc are fixed in the medium term. So I dobt worry about them.
Electricity & heating I have some control over (eg turn thermostat down, have shorter showers, be mindful of using oven, hob, kettle, try and line dry clothes, wash full loads, etc).
Petrol I have a little control over- eg drive more efficiently and as little as realistic.
Food shopping I have lots of control over - buy porridge oats and a bag of sultanas, make lentil soup, look online for cheap recipes, figure out the cheapest options (eg frozen or fresh), limit treat foods, etc. Its by far the easiest way to make consistent, regular savings.
Try not to eat out for birthdays - if it costs you 120, five times a year, that's 600. Maybe takeaway instead?
Subscriptions... try and cancel everything or as much as possible. Kids activities cost me a fortune, drop whatever you can. HOWEVER, if you cut everything to the bare minimum it's hard to keep it up.
Then, the obvious DONT BUY ANYTHING - readjust your idea of "essential". Obviously basic soap, deodorant, shampoo, toothpaste, etc. But, do you need more than "one to wear, one in the wash"... you probably have that already, so does anyone actually NEED new top? House things - nope, don't buy anything until your debt is gone. Don't look for bargains, just don't buy it.
Personally, Id aim for discretionary spending to be ZERO until your most expensive debt is under control... thats "aim for" which wouldnt necessarilybe achieved. Obviously DC birthday gifts are essentials, and realistically you're not going to have no treats for 2 years. But for a few months it should be OK.