Sindy can I please get your opinion on the following idea?
My opinion is that having the same IP subnet on two different bridges (or any other interfaces) is a ticket to a madhouse. I'd have to replicate that configuration to see how exactly RouterOS works with ARP in this case, because the routing needs to choose the right bridge (interface) for each destination IP address. The arp table contains mappings from an IP address not only to a MAC address but also to an interface, but whether the ARP request used to populate the table when it contains no record for that IP address yet is sent out all interfaces whose subnet contains the destination address is out of my knowledge.
It is also out of my knowledge whether broadcast packets (which are the very reason why you venture all this) are forwarded between interfaces which bear the same subnet; normally, broadcasts are not forwarded between connected subnets, so an exceptional handling would have to be implemented for this special case. Maybe it has been implemented (as you say that everything works) but you have to check.
DHCP normally sends the Offer out the same interface through which it has received the Discover, but it is again out of my knowledge how it works when the same MAC address already has a pending lease.
But at first place I don't understand what made you go this way. In my suggestion, everything was in a single IP subnet on a single bridge, and the group to which the device belonged was determined by the SSID it used, translated into a wlan interface name. Were you unable to make it work? Or you wanted to strictly separate the address pool for each SSID?