There is no correspondance between ports and players. You can have 1000 players on 1 port or 1 player per port... doesn't make a difference (though in the latter case, you could only ever have 100 players).

No, the problem is that if you have more than one server on a machine, each has to have it's own port for clients to connect into. The current bug AFAIK makes it so that you can only assign one port no matter what. This is why having multiple servers on one computer was problematic. Furthermore, it is my guess that 2300 is the default port assigned.

Try this:

Set the -port of the server directly to 2333 and try to connect with a client. Did it work?
Now, set the -port again to 2333 and try to connect with a client and set THEIR -port as well. Did it work?