This is a major issue amongst parents of multiples. We are back on another child because we are terrified of having twins again (or more!). Most people don’t worry about their when planning a pregnancy!
On the plus side you have more options than most and I agree, you can’t have it all. For a few years something has to give.
One good way to look at it is seeing childcare as a fixed cost until all the children no longer need it, rather than a monthly amount. Add up the likely childcare costs until the twins start school and then the cost of wraparound care until they’re old enough to not need it. Let’s say for arguments sake it’s £12k.
You could extend your mortgage for that amount and extend the term long enough that your monthly payment doesn’t increase. Put that extra money in a savings account and use it each month. Or you could look at how much of the £3.5k you’re currently paying in mortgage and childcare you can afford, and extend your mortgage by less.
You’re really looking at a couple of years added on, if that.
Or you condense hours, take an extra amount of leave, get a childminder instead etc. Only you know what compromises you’re happy with but you have to make some somewhere.
I loved my job too, albeit part time but I’ve recently had to take a few months off and may be unable to return. My twins are both autistic, amongst other things, and I’m currently focussed on trying to get them into specialist schools. They need all my focus right now. I didn’t plan for things to go this way obviously. Unfortunately we can’t plan for these things.