Hi, I assume that your routers are lxd guests, and you want them to manage your network, not lxd itself. I also assume that you are using single non-clustered lxd host.
Create 3 bridged networks:
lxc network create lan1 ipv4.address=none ipv6.address=none
lxc network create lan2 ipv4.address=none ipv6.address=none
lxc network create routers ipv4.address=none ipv6.address=none
Create profiles:
lxc profile create p-router1
lxc profile create p-router2
lxc profile create p-client1
lxc profile create p-client2
Add storage and network devices to profiles:
lxc profile device add p-router1 root disk path=/ pool=<storage-name>
lxc profile device add p-router1 lan1 nic name=enp5s0 network=lan1
lxc profile device add p-router1 routers nic name=enp6s0 network=routers
lxc profile device add p-router2 root disk path=/ pool=<storage-name>
lxc profile device add p-router2 lan2 nic name=enp5s0 network=lan2
lxc profile device add p-router2 routers nic name=enp6s0 network=routers
lxc profile device add p-client1 root disk path=/ pool=<storage-name>
lxc profile device add p-client1 lan1 nic name=enp5s0 network=lan1
lxc profile device add p-client2 root disk path=/ pool=<storage-name>
lxc profile device add p-client2 lan2 nic name=enp5s0 network=lan2
create and start Instances:
lxc launch <image-name> router1 --profile p-router1
lxc launch <image-name> router2 --profile p-router2
lxc launch <image-name> client1 --profile p-client1
lxc launch <image-name> client2 --profile p-client2
Now you need to do manual configuration of ip addresses and route tables from inside of your routers.
Have fun 