Maybe install software on presenter's laptops instead of using VGA cable?
I understand that you are having some issues with content when connecting through VGA. What model unit are you currently using? Have you tested this with more than one VGA cable at this point? If you are looking in the camera settings menu of the unit what is the camera source set to for the PC input? Are you set to Content People or Both? What software version is running on the unit currently?
Another question, Under Cameras>Content> Do you have your content set to Sharpness or motion?
Setting this to Sharpness will give you a much better, clearer image.