I think the thing people seem to be missing is they for some reason think his household is better off.
They aren’t, they are worse off with 2 extra people to pay for and have lost a whole parents wage. They have lost around £1700 a month in wages (based on previous cms calculation)
So house 1 is £1700 a month worse off
House 2 is £250 worse off
If NRP worked evenings around his wife’s work they could potentially make up maybe £750 at most I would think (he won’t be able to work nights if he needs to be up to care for twins whilst SM works so will only really have until 11pm to work. He pays £250 to ex. Left with £500 (realistically less as travel work costs etc to add to this) = house 1 is still 1k worse off every month - this impacts all 4 children 2 of them 100% of the time and 2 of them 25% of the time, plus by the time the 2 eldest get there on a weekend the whole house is likely knackered playing tag team all week, so they don’t get the best of their dad either.
House 2 is now back to previous standard. Financially and OP still gets to stay home, gets plenty of time without the kids.
Or
NRP becomes SAHP - household still take the hit of a £1700 loss
House 2 takes the hit of the £250 loss
But everyone gets the best of their parents in time.
Or
House 1 decides to become SAHP takes a £1700 but can be more available to his eldest DC also so can do every weekend allowing their mother to work and pick up sick days etc to help.
House 2 loses £250 but can now work easier as dad is more available (yes there is a distance but weekends it’s ok). So OP can work sat and sun, no working in the week and no other kids to look after, childcare available at least 15hrs for youngest and full time school for eldest so has some free time still. OP can earn around £600-£700 doing 2 days a week minimum wage.
House 1 remains £1700 worse off
House 2 is now £400-500 better off.
I don’t see why this is so difficult to understand?
When NRP twins are 3/4 and get some free hours, he can go back to work the exact same and pay even more on top so house 2 will be even better off in the long run.