Routers don’t like being in the same IP pool if they both want to control dhcp. Only ONE dhcp server per pool. The dhcp server should also be the gateway. Eg 192.168.0.1
You can add another dhcp but it must be on a different pool eg 192.168.1.1, again it will also be the gateway to THAT POOL ONLY. That router will do the forwarding to the original gateway 192.168.0.1 automatically.
So long as they are on the same subnet (255.255.255.0) they should be able to communicate with each other. If not then try installing the upnp plugin to mitigate firewall problems.
If you are intent on having the gl router as a ‘dumb’ router then you can disable the “authorative dhcp” in LUCI, which should allow the router to play nice.
Good luck.