To connect two Omnias (site-to-site) you can just use masquerading (for the WireGuard interface) and putting the relevant subnets into the allowed IP configuration for the two “peers” (the two Omnias).
This is similar to the configuration I have set up. It assumes that the WireGuard interface is
# Peer 1 config wireguard_wg0 option public_key 'public_key_of_peer_2' list allowed_ips 'VPN_IP_OF_PEER2/32' # example subnet served by peer 2 list allowed_ips '192.168.40.0/24' option route_allowed_ips '1' option endpoint_host 'endpoint_ip'
And for peer 2
# Peer 2 config wireguard_wg0 option public_key 'public_key_of_peer_1' list allowed_ips 'VPN_IP_OF_PEER1/32' # example subnet served by peer 1 list allowed_ips '192.168.30.0/24' option route_allowed_ips '1' option endpoint_host 'endpoint_ip'
Of course you need to make sure that the WireGuard interface is properly masqueraded.