If the radios are running in their "out of the box" state, it's probably on 464.500 or 464.550. Those are two VERY common UHF business itinerant frequencies. It's no wonder you are getting interference.
There are a lot of other UHF itinerant channels to choose from. Using something other than what the radio has programmed right out of the box will probably fix the interference issues. Set a PL/DPL tone other than the first one, and you'll probably be good.
As for licensing, if you have not done it before, it's probably going to be very frustrating. It is possible to do it on your own, but those new to the industry rarely are successful on their first try. Since these radios belong to the school, let them pay for getting it done legally/correctly. There are plenty of companies that will assist you for a small fee. They'll find a suitable frequency and file all the paper work for you. I'd strongly recommend having the school administration pay to have that done. It really is quite painless and much, much, much cheaper than an FCC fine.
Contact these guys to get started: