Both can probably help and fit the needs.
However, if you know you're requiring only 1 application for a fixed limited 5 users - I would more go on 1 unique virtual machine where you can adapt the required RAM/CPU resources that you will need for your 5 people. It will be faster to configure and deploy. Especially, if you know that you can do "concurrent" scenario (and not a 1 VM).
By default, you can have 2 RDP sessions opened at the same moment on a server. So, you will probably need CAL RDS licences to cover your 5 collaborators. More details.