If you need more / different isolation, you're going to need custom nftables/ebtables rules.
In another model you could drop each bridge onto a unique vlan, and firewall them.
There's tons of options out there.
Anyway, if you had more specifics to go off of, there's plenty of network engineers and kubernetes/docker admins floating around willing to help - maybe start a Ask HN post?
You're still offering suggestions I said I didn't ask for. I'm sure you're trying to help, but at this point you're coming across as passive-aggressive.
In another model you could drop each bridge onto a unique vlan, and firewall them.
There's tons of options out there.
Anyway, if you had more specifics to go off of, there's plenty of network engineers and kubernetes/docker admins floating around willing to help - maybe start a Ask HN post?