@plym perhaps I'm miss understanding your setup, or maybe miss understanding docker, but as many containers as you like can have the same internal port as long as the host port isn't the same. So there should be no need to change it.

Container 1 - 80:90
Container 2 - 81:90

This should work just fine. Number to the right is internal to each container with their own virtual network adapter. Number on the left is the host which just has it's singular network adapter. https://stackoverflow.com/questions/58449359/why-multiple-docker-containers-can-have-the-same-internal-port

@plym then if you're being safe and running a reverse proxy condom you can just map a subdomain or whatever to whatever port on your host you like. So the host port doesn't need to match the internal container port nor does it need to necessarily be 80 on the host machine.