My advice is use PAM. Wipe down the outside of the boas cage as well as the upper and lower rims of the tank and the table. That will hopefully keep as many mites contained in there as you can.
Then throw all the cage stuff into zip lock bags and hit it with a shot of PAM and seal em up and put them in the garage for 3 months while you are treating the snake.
For the cage, just leave a hide and a water bowl. Use paper towels or newspaper and spray them with PAM. Spray the inside of the cage and cover it and let it simmer for 15-30 mins. Then replace the snake. I leave the water bowl out overnight on the night of fresh application. Do this every week for 3 months.
And for the other snakes, i would apply a one time treatment to the bedding. Take the snakes out, water bowl and then give the inside of the cage a light shot and let it dry. make sure it is dry and then replace the snake. Leave the water bowl out overnight. Then wipe down the outside of the those cages too as well as the table or stand they are on.
Thats what i did the one time i had to deal with mites when i brought home a hitchhiker and Luna got got mites. Luckily they didnt spread and i moved Luna upstairs into a spare bedroom for quarantine.
I convinced her that we needed to use PAM. We did as you suggested. I also noticed she was about to shed. Will the mites burrow under the loose shed to keep safe or will they be killed either way?