We have similar kind of requirement and need to setup multiple port (few duplicate within instances) for two instance running on same cluster node

Could you please let me know if suggested changes ( Filrewall & SQL server config mgr ) has been implemented in ur env and its working fine.

if you have setup in ur env then request you to share the steps and feedback how its running so far.

fyi.. my requirement

server\instance1 - Port 1433, 1434

server\instance2 - Port 1433, 1435

Enabled protocal - Shared Memory, TCP/IP, Named Pipes

Thanks in advance for your response & help.