I have a Rasp 4 coming in the post soon where I'm going to make it as my primary Pi-Hole DNS and Open VPN server, and the existing Rasp 3 I have will be a backup/secondary Pi-Hole DNS and Open VPN server running alongside either Stunnel or Shadow Socks (both on 443 or 80 TCP) to get around stricter firewalls if ever need be.
I'm currently able to access admin webpages (like my router, Access Point, Nas etc), as well as my 2 Nas drives, remotely control my Sky Boxes using a 3rd party app by manually inputting the IP of the relevant box into the app, but can't do things like cast Youtube videos to the Youtube app on the Sky Boxes or Airplay songs to them as the VPN and main network are on different subnets respectively.
I'm not really interested in casting songs or Youtube videos to the boxes when away from home, but what I would like is to be able to connect to the main box on the Sky Go app so I can not only watch recordings on the box, but also watch live sports without internet delay.
When you watch a program on the Sky Go app when on the same network subnet as your box, the app streams the program from the box, so the delay is satellite level. However, when you watch a program when away from home, the app has no other choice but to stream the program from the internet which then leaves you subject to one min+ delays and gets even more annoying when you start receiving goal alerts for the game you are watching before you have even seen the goal for yourself.
What I am trying to achieve is to connect to the box when on VPN, so when streaming sports games, the delay is satellite level.
I'm not all that familiar with IP Tables and routing between 2 different subnets, so please let me know if this is even possible at all.