In the scope of wireguard it’ll just be a matter of you building appropriate firewall rules.
Since you want their internet traffic to go through you then i assime you’re effectively pushing a 0.0.0.0/0 route to your clients. You then need to add firewall rules on your server to block traffic to its local subnet and in the future allow traffic to only your jellyfin server.
This is also pretty simple and nothing wrong with that setup.