To connect them directly, you'll need to pick some interface such as ether5 on each router and hook them together with an ethernet cable. Before you connect the two routers, go into each one and make sure that ether5 has master-port=none and is not configured as a port on any bridge in your configurations. (The quick way to check is to make sure that there's no S in the flags for ether5 in the Interfaces display)
Now you just need to create a "transit" network between the routers - let's say that the transit network will be 192.168.255.0/30
On R1 - add the IP address 192.168.255.1/30 to interface ether5
On R2 - add the IP address 192.168.255.2/30 to interface ether5
Now connect the cable, and you should be able to ping 192.168.255.2 from R1 and ping 192.168.255.1 from R2. This proves that the link cable is working.
Then go into your firewall NAT rules and make sure that packets going out ether5 will not get NAT translated.
Make sure that the filter rules on each router will allow the type of traffic you wish to permit when it goes across ether5
Then tell the routers to use the link to reach the other room's LAN by adding static routes in the IP routes menu.
on R1, the destination will be 192.168.2.0/24 and the gateway will be 192.168.255.2
on R2, the destination will be 192.168.1.0/24 and the gateway will be 192.168.255.1
Note: If the routers have static IP addresses on their WAN interfaces, then you don't really need to add this direct cable and transit network. You could just add the static routes like the last step above, but set GW = the wan IP of the opposite router. The routers will need to have exceptions in their NAT rules so packets w/ the opposite LAN as the destination will not get SRC-NAT translated.
(if your outbound NAT rule is simply set to do masquerade when out-interface=ether1, you can just modify this rule by adding the criteria dst-address=!192.168.2.0/24 on R1 (and !=192.168.1.0/24 on R2)
Your forward filter rules would need to permit the desired services based on src IP address and not interface name in this case.
When given a spoon,
you should not cling to your fork.
The soup will get cold.