DH and I earn very similar to each other - 40k a year each and neither of us dropped to PT but we do flex around each other, he works 8-4 and I do 9-5 meaning I can do most school drop offs and he can collect from afterschool club. we've just come to the end of 2 years of full time nursery fees (over 1k a month) for the little one, we've still not gone without holidays (barring 2020-2022) I am going to be quite frustrated that we wont have as much left over to recoup the non existent savings had to use when DS2 was a baby, but - we purposely only had 2 children as we knew 3 would be the biggest stretch.
Net joint income is around 5000 after taxes pensions and student loans, compared to your costs -
mortgage - £1200
Food, groceries, £550
Electric, gas and water bills £200
Loans on 2x 5+ year old cars £3400 (9 year old fiesta and 6year old family car both will be paid off in 18 months)
car insurance - £50 for both
£100 a month fuel to commute to work
car tax, servicing, MOTs and repairs - £50/month
buildings and content insurance - £25
Broadband - £25
cheap mobile phones - £45
Life insurance - £40
Clothes and shoes for us all, including school uniforms - £30 a month into an account and stuff only bought when needed
school trips and donations and endless dressing up outfits required - Not regular at all, maybe £10-15 a month
swimming lessons for children £65
school meals - £2.85/day 2 days a week. Ds2 in KS1 so free.
Clubs for the children - Karate, £65 a month
A budget birthday party and £100 present for each children their birthday (usually next size up bike) - say £200-300 per child?? (that's more than we spend but breaking it down) so £40 a month
miscellaneous - card and present when attending classmates party and small present for children in family - £20 a month
every month something like repair to boiler or equivalent - not experienced this on an every month basis, just bought a new microwave for £35
professional fees for employment - mine are covered by employer
£100 per child at Christmas - £50 a month away for xmas costs
Petrol to visit elderly parents - included in general petrol costs
Interest free loan for furniture (although most 2nd hand bought off marketplace) - £35
Childcare (wraparound) £200
On our income that leaves £1700 a month 'spare' on yours its more like £1200 a month. We've had 3 holidays this year (weekend in a caravan at easter, 7 nights in center parcs, and a 10 day foreign AI holiday) time away from home and work is a priority for us and we stick to our budgets across the board to ensure we can have this.