Just set them in a bucket of water and rehydrate the flesh.you could even Leave them in the and let the skulls macerate. No bleach. It never stops whitening and it will turn the bone chalky.
Depends on the time frame you want, and quality at the end.
If you want fast and easy, and don't mind a fake skull, go the fake skull route. I've only done 1 this way because my dog got a hold of my deer skull mid cleaning while I was taking a break and ate the face off. I personally don't think it looks as nice as the natural skulls- but is much less work.
If you're willing to spend some time and prep on them and want more natural looking, then choose an option:
1) Soak them for a couple days and re-hydrate the meat, but don't put the antlers in the water. Then continue with your original plans of powerwashing, but may need to do some extra re-hydrating or scraping. And don't forget about them while soaking again.... or it will turn to the point of (see next)
2) maceration. This works best if the water is kept warm with a tank heater. Put in a bucket/container of water (leaving antlers out of water) and leave it until everything rots off (which stinks, and you'll have to let it air out outside once finished because it'll stink too much to want to keep in house, which can take quite a while)
3) You can boil them (leaving antlers out of water), which helps rehydrate- then powerwash and scrape everything off. I would recommend rehydrating a couple days prior to boiling. I think it will make that process quicker.
4) leave it hanging where it is- everything will eventually fall off.
After any of the 4 above options:
to get it white: "bleach" it with a kit online or soak in hydrogen peroxide.
All is not lost, you just have a little more work and elbow grease required to do now that it has dried. But at least you skinned them- that would make your job MUCH more difficult if you hadn't. Good luck.