If you want 5 pc’s to be able to be accessed remotely, rdp is definitely usable. I use it to access my home pc from work.

I have a netgear Orbi mesh network for my home (would have gone with other networking hardware knowing what I know now), but it has a built in vpn server.

You could get a router that supports vpn, and then set up access controls for the rdp protocols on each desktop, and give your interns the vpn configuration information needed so they can vpn into the network and rdp the machines “locally” without opening up the rdp port to the internet. Just make sure you segregate those computers from the rest of your personal network, the parts you wouldn’t want anybody to have access to.

Depending on the software you’re using, it might make more sense to set up a hyper visor type system, where you have one machine powerful enough to run 5 virtual machines, and then you can grant access a few different ways.

Either way, if this is big money, it might be worth it to hire a consultant to help point you in the right direction with what you even need to learn.