sleeponeday - it's usually the lowest paid partner who is the one who's wage is set against the childcare costs. Sadly, that's usually the mother, but it doesn't always work that way, I know a few SAHDs who have made the same calculation.
OP - if your DH can work on a Saturday, for a year it might well be worth him requesting a full day swap to working all day Saturday and having a day off in the week instead so you are only paying for 2 days childcare, with him having to work on Saturdays for part the day anyway you aren't going to be able to do traditional weekends anyway, so why not pay for 2 days care rathr than 3? It's worth an ask.
It is such a short time for you, I assume you can get your twins in the cheaper nursery at 2, and then make a profit (and your eldest will be entitled to 15 hours free then, right?). Also worth looking at nanny costs, most are cheaper than nursery for 3 DCs, but that is a fixed cost, so the price won't fall when your eldest gets their 15 hours preschool, just that the nanny will have to drop them off and pick up. (but still be paid the same with just the other 2).
I gave up work when it became apparent with 2 DCs I'd make a loss but also my job was changing to something more junior (even if the job title was staying the same) so it wasn't something that was 'keeping my career going'. A year on I miss working, and am considering looking for work again from September as DC2 will be going to pre-school (and as we'll have to pay for pre-school anyway, I'm knocking that off the childcare bill in my head as that's what we'd pay if I was at work or at home! It's a bit 'cheat' to make me feel better about looking at jobs where i'll work for a loss for 2 years until DC2 is at school!). But I think it's very hard to leave your babies and be at work having a bad day thinking "I'm not even making any money from this."