Since you are having difficulties installing your two Slingboxes on the same network, I will recommend you to reset the Slingboxes and try to configure those again. Use the Web-Based SlingPlayer to install the Slingbox PRO-HD and the SlingPlayer Desktop for the Slingbox Classic.
Feel free to use the following links to enable the Internet Viewing setting, therefore you can watch those away from home. You should use a different IP address for the units, the setup will show you which is the Slingbox IP address of each Slingbox, and also use different ports for both.
I hope this helps.