This just something that you can try, on the address bar of the browser type the public IP followed by :6000 or :6001 respectively.
For example: http://69.66.218.208:6000 and http://69.66.218.208:6001
If you have two virtual servers with one mapping public port 6000 to private port 21 and another virtual server mapping public port 6001 to private port 21 for the private IP of each computer, I think that would work.