In that case use VLAN to separate different functions.
One single bridge.
See here for de facto tutorial on VLAN:
http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1
(read it, digest it, read it again, …)
And here for base setup of vlan in capsman:
https://help.mikrotik.com/docs/pages/viewpage.action?pageId=46759946#WifiWave2(7.12andolder)-CAPsMAN-CAPVLANconfigurationexample: