I beleive DD-WRT only supports VLAN IDs between 0 and 15 inclusive, so you need to change your VLAN 20 to be within that range. Also use the VLAN tab to assign ports to each VLAN.
Once you have the VLAN IDs and tagging sorted, you then need to create an additional bridge under networking tab. Assuming the VLANs are separated, assign one VLAN to each bridge. I don't think you need to use the VLAN tagging option.
I beleive DD-WRT only supports VLAN IDs between 0 and 15 inclusive, so you need to change your VLAN 20 to be within that range. Also use the VLAN tab to assign ports to each VLAN.
Once you have the VLAN IDs and tagging sorted, you then need to create an additional bridge under networking tab. Assuming the VLANs are separated, assign one VLAN to each bridge. I don't think you need to use the VLAN tagging option.
I'm using DD-WRT in access point mode so it may be different if you're using it as a router.
I'm not sure what the VLAN tagging option is in the networking tab, but I haven't used it.
I think your problem may be in the VLAN tab. If your VLAN IDs are 1 and 15, then you need to have 1 and 15 checked in the VLAN tab for the corresponding ports, not 1 and 2.