Kittens in heat due to be spayed

[Topsy15]

Hello, some help please!
I have two kittens they are just over 6 months old and are booked in to be spayed tomorrow. They have been behaving very strangely, very clingy, more affectionate than normal, extremely vocal and lots of yowling, changed appetites, one more than the other. I now realise it is likely they are coming into season! What is the best thing to do? I know it is risky spaying while their little uterus is swollen. I have cancelled the booking for the worst of the two, the other one has been behaving a little bit oddly but nowhere near as bad. Is it likely they would be 'in sync'?
I feel awful because I wanted them to go in together but if they are going to cycle in and out of season feel it's sensible to get the one who is okay done tomorrow.
I'd really appreciate some help from someone more experienced! I can't find much help online. Thanks 😊 🐈

Can you not ask the vet that was going to spay them? They may do it during heat anyway

A lot of cats are spayed while in heat, while it is a little more work (as everything is more swollen with more blood flow), it's not particularly risky. Best to ask the vet's for advice?

In the meantime be VERY careful to avoid escapes, they will be absolutely determined to slip out while in season.

We spay regardless and most vets should. But yes, make sure they are on total lockdown. Don't leave any windows open, even a crack. Be ultra careful when opening doors.

Take them both in tomorrow as normal.

Thanks everyone! Super helpful. Yeah they've never been outside before so being so vigilant... I just find their behaviour hilarious I've never had a young female cat before

Should be no problem I did two sisters yesterday one in heat one not. I had to pull slightly harder to tighten the ligatures on the ovarian pedicles for the in season cat than the not in season cat. Really it maybe added 1 min to my overall op time, nothing significant.