so you need a spreadsheet.
one column basic bills with fairly static prices. like the list you're listed here. do you have house insurance?
then a column for food shop. include kids lunches, take aways, odd coffees or coffee shop weekend treats, all those incidentals.
have another column for people spends - clothes, uniforms, hair cuts, school trips, birthday and Christmas gifts
another column for everything else.
start Dec 1st and go online every few days to upload it. you'll soon see where your money is going.
any cash taken out try and list under one of those categories
do you get child support or child benefit?