You might as well get into the mindset of getting a rack setup. You have three snakes now and the simplest setup you can go to is a rack setup. Think of using tubs but in a shelf with identical heating across the board. It is going to be your best option.
People on here that use rack setups can give you all you need to know.
Yes for the temporary housing you can go with tubs and heat mats and thermostats but I highly recommend migrating to racks as soon as you can.
Ball pythons must never be housed together outside of a breeding pair about to mate and even that is only temporary. I am glad you are understanding the importance of keeping them separate.
Get temps, humidity, and their sense of security under control and you can start acclimating them in no time. Might take a few weeks to get them eating regularly so waiting to handle them until they have eaten 2-3 times should be what you shoot for.
For digital thermometers and humidity gauges, AcuRite is the company to use.
I second an IR temp gun, you will have such great peace of mind owning one.
Get this one, it is flawless
https://www.amazon.com/gp/product/B00DMI632G
Oh and welcome fellow Tennessean!