Need help with a question about remote desktop gateway across a network

Ok so am working on a project for school where my group is designing an implementing a solution for a made up company. the network is almost entirely virtual in vmware and connects to the schools internet. Due to certain rules and requirements we are limited on certain actions. I will explain the problem I am trying to solve.

I have a virtual router connected to the schools network which is where I work from( we Nat to this network and it is treated like the internet, but obviously its not). the router connects to a physical network (which will be ignored for this problem) a group of subnets for host VMs and a services network. I have a windows server with a rdp gateway as a possible way to allow users in the school network to remote into the host VMs but I can not get it to work. The problem is the cert (self signed which I was able to add to root trusted certs on the client machine) does not match the gateway IP in the client computer because I have to use the WAN IP to reach the server because the domain is private so the FQDN wont work and the routes are also not advertised to the schools networks (it is treated like the internet basically.)

My question is what is the best way that you know of to accomplish remote access to the host VMs? Can I make my private DNS advertise to this network somehow or perhaps make the WAN IP port forward to it so that either the rdp can connect to the gateway without an issue or route the client DNS to my server? Maybe I can set up my router as a DNS and list it as the clients DNS? I have tried a lot of things and I keep running into solutions that would require either a direct server connection to the internet (not allowed) a public domain (not applicable) or 3rd party certs(not really in the scope of the project and require public domain)

other notes: RDP works if i just port forward to an individual host

I tried to edit the client hosts file but do not have permission.

I am not a professional but am a student so some obvious things may not be obvious to me.

sorry if this is a bit jumbled but I am having more trouble than I thought I would and have gone a bit loopy after messing with this the past few days.

Any suggestions or ideas are welcome thanks for your time and help.