I think you are really asking two questions:
(1). How can I VPN in to my home Roon Server.
Answer, at the moment Roon does not support this. Some other users may have gotten something running and they might be able to offer insight.
(2). Can I play music from Roon on my iOS device, iPad or iPhone.
Answer, at the moment Roon does not stream music to iOS devices. This is due to issues with Apple’s OS, the framework Roon uses and some other issues. There are several threads detailing this if you care to search, here is one example: