you can use TROWinHttpServer.
latest beta contains an improvement for this server, that allows to launch several servers on one port.
another possibility: convert your services to isapi dll and use it under IIS. in this case, URL can be like https://server/path/server_name.dll
we have the MegaDemo sample that contains usual server and isapi dll.
the 3rd possibility: use ROServer.OnCustomResponseEvent event. proxy server will accept requests from all four clients and sends them to correspondent servers, later it will send responses back.
see more at the Using OnCustomResponseEvent in a ROSDK Server post.
also examples of usage can be found in linked threads.