We have to use remote SSH forwarding of port 10000 and local fwd. of 7869 to debug PHP scripts running on a Linux Apache server. In this mode, when one user has a debug session open (and a ssh session to the linux machine running Apache with libphp4) a second user cannot open a debug session to the same machine, so that means that although we have bought several licenses,we can actually use only one of them. What would be the solution to this situation? Any dbg settings in the [debug] section of php.ini? Any other forwarding method?

Thanks

You only have to forward dbglistener's listening socket to the server.
Suppose you have 3 developers in your team.
Each runs DbgListener on different port (10000, 10001, 10002).
Each runs ssh that forwards this port to the same remote port (namely 10000, 10001 and 10002). They also have to set these ports in their IDEs: tools->settings->debugger->debugger port.
Php.ini settings should be adjusted to allow connections on these ports:
debugger.ports=10000/3