Please be advised, placing the Guest WAN's gateway on IP Table No. 2 will make the Guest Network isolated from the other networks on your router, as it will no longer use the main routing table. This can be fixed by adding more detailed rules.
Thank you for answering my question.
Am having problem applying IP rule so Guest LAN traffic is using Guest WAN. ip route show table 2 does not give anything back so am guessing the rule has not been applied. Am I supposed to put your config in /etc/config/firewall and then run a /etc/init.d/firewall reload?
I do think the reason this does not work is because both guest_wan and worker_wan is using the same gateway. It may not be clear but see the first post on the IPv4-addresses, 198.51.100.13/24 is worker_wan and 198.51.100.14/24 is guest_wan. meaning both is using gateway 198.51.100.1.
The trick am after is to have all from guest_lan use a different outgoing IPv4-address. In this case 198.51.100.14.
in the firewall you should turn on ip masquerading for the guest wan (can do it in luci with a checkbox) that should cause it to use the guest_wan IP as the ipv4 for outgoing connections through the guest wan. I think this might be your problem.
This setup works if WAN interfaces is using different gateways. That is because of the config route rule that match everything on route table 2 and sends it to defined gateway in that rule.
Thank you lleachii for solving this question.