That makes so much more sense.  You are most likely running DHCP on both of your routers which can cause lots of headaches.  For now I would remove the DD-WRT device.  Connect your laptop to your home network to verify what subnet range is.  It should be 192.168.88.0/24.  If this is correct configure the light beams to be something in the 192.168.88.0/24 range.  Something that is not in use by another device!  Then take your laptop and plug it directly into the LAN port of the remote/station light beam.  You should be able to connect to the internet.  If this works install the Unifi controller on your laptop so you are able to configure the Unifi Mesh device.  Use a second POE adapter to power the Mesh and use a ethernet cable to connect the LAN ports of the station radio and the Mesh radio POE adapters.  Use the Unifi controller to program the Mesh radio.  I'd leave the DD-WRT out of the picture for now.