I don't even know if my router is capable of running many players on one port.
All games run on one port.
Being able to run many players has nothing to do with that.
For Blockland this port is 28000.
Some servers run multiple dedicated blockland servers, and they use multiple ports. One for each server.
But everyone else just has to port forward that one port.
Plus, you can port forward a range of ports to a server at the same time.
And I really suggest trying to find access to your router.
You will keep running into problems with UPnP.
It is kinda flimsy in that way.