It's a little more complex than that for any non-trivial layout where some containers do need to talk to other containers, but most don't.
Yes, if they need to talk, share namespaces.
If you don't want a generic but true answer, don't ask a generic question and then be upset when the responses don't have enough detail about your specific situation that you hadn't described :-)
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?
Your responses have confused me so much I showed them to my partner, who is also confused.
I'm not sure why people are replying to my comment with solutioning and trivial suggestions. All I did was encourage the thread OP to publish their notes. FWIW I've already been through a lot of options for solving my issue, and I've settled on one for now.
Because your comment didn’t say you solved it and you asked for notes without any polish as if that would help.
If you want multiple participants, you use bridges, which are roughly analogous to switches.