Suggest read this article for a fuller understanding of the setup!!
http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1
The quick answer is that there is no need to create a second bridge,
simply put all WLAN bridge ports on the same bridge.
They are separated by access based on SSID and firewall rules on the router the capac is connected to!
OH OKAY,… this may not be just an access point???
However, what is confusing is that you seem to be creating a DHCP server on the capac?
Is this also acting as a router??
Do you have a network diagram you can post??