VPN Access for only certain apps

Hi Folks,

I want to set up a VPN tunnel from my parents house, through to my private network, so that I can share my media server.

The catch is I want it so that only the media server client (Jellyfin) to connect through the VPN, but I want ANY Jellyfin client on their local network. So if Mum opens it on her tablet, or Dad opens it on the TV, it does not matter, it will fly down the VPN tunnel, and everything else will exit to the cloud as normal.

I know split tunneling, but i've never done this for a whole LAN, only single devices, and only using commercial VPNS (Currently use Proton VPN). Would this be possible via only our routers (assuming that they support wireguard VPN) OR would I need something extra to act as a DNS Server or something? I have an old raspberry pi sitting around, so I could throw that in there if need be

Am I over thinking this? How would you go about it?