Thank-you for contacting Slingbox Forum. We are sorry you are having this issue.
You can have more than one Slingbox on a network.You will need to have each Slingbox set at different port location. Here is a link to assist you with that How to use the Slingbox Network Setup Assistant to help configure your router.
Also, the following links are about the connection issues. Review the following links PRO-HD tech spec and A slow Internet connection at home can affect picture quality when using Internet Viewing.
Hope this helps with your issue.
Sling Moderation Team