You need to set up a publicly accessible device (in this case the VPS) as your IPv6 gateway
So you set up your VPN connecting your network to the VPS (should probably be set up from the router) and set your router to advertise an IP adress for the VPS which is routable from your local network as the gateway address (and should probably also run DHCPv6 for your network)
(note, I have not set up this stuff myself so I can’t help with implementation details)
The main program is open, but the development tools are not