I will add that if you run in to the issue of everything being wet and damp preventing them from dust bathing then you may need to make them a spot. I’ve had to do that before in the really wet times of fall here
I usually add some diatomaceous earth to their usual dust bath spots and it does the trick. If you are going to tractor supply anyway it is very cheap and your birds will thank you for it.
As for sevin dust I’d ask a veterinary specialist because i don’t know if them breathing it would be safe.