Just get 1 router to do it all. Grab a Mikrotik. Set primary router for your network then add a metarouter to handle the VPN. Bridge the metarouter and router LAN together, set different ip range. Then on the router set dhcp for your regular LAN, then set static dhcp for the devices you want to relay via VPN on its ip range. That is how I did it, works awesome for relay VPN. Easy switch on static ip systems too, just change the ip address. Keeps connection open all the time as well.
