They CAN have water, you know -- my cats get more upset about no water, than no food down... and my vet told me that WATER is OK the night before.
I have had MANY females spayed, over the years, and none have ever had to have the "cone" you are talking about.
MOST vets here in the US do the internal stitches with dissolving thread, and "GLUE the top layer of skin, to prevent them from "pulling at the stitches" now-a-days -- but over the past MANY years, the females I had spayed who had external stitches seemed to LICK at them, but never pulled any out. (I suppose when they PULL at a stich, it probably HURTS, so they stop on their own, if they do it, at all.)
I'm sure they will both do fine
The procedure is MUCH less severe for the males than the females, and I still want to remind you, the JUMPING is the most "worrisome" -- the females CAN cause themselves a hernia, if they are too active the first couple of days...
Keep us posted, I'll be thinking about you, and THEM tomorrow
LaVon