Tun to tap reconfiguration

[wedge1001]

Hi,
due to some changed requirements, i'm now (more or less) forced to move from tun to a tap-Network.
mainly due to some broadcasting-things (and me trying out new things)

My network now looks like this:
3 Pfsense-Systems. one Pfsense on the Internet acting as Server and 2 pfsense-clients on location a and b (my apartment and the my parents' apartment )
each location does have it's own subnet and own dhcp, dns and internet-connection.
(see attachment)

my Problem now is:
if i change to a tapped-network both locations get into the same subnet (as far as i understood this) - this isn't my problem and can be configured.
my Problem is now that if i don't want to route all internet-traffic from location b through the internet-connection at location a.

is there a way to get them into the same subnet with a bridged setup, but forcing them to use the local internet-connection?

Since there are a fluctuating number of devices in each location a mac-setting in the DHCP isn't an option.

I'm thankfull for each idea you may come up with