Hello,
Landscape and portrait are going to show differently, the layout is determined by the width of the screen, and it gets much wider when you turn the device. You can make many adjustments under the layout tab in Vertex for when you want items like the right column to combine, or when you want the row positions to combine into smaller groups.
A tablet width is defined at 750px, it's meant for smaller tablets like the iPad mini. The standard iPad is much larger screen and can usually handle items like the columns in the same position as desktop, in fact it's the same size as many smaller laptops. But like I said above there are options under the Layout page to adjust when certain items combine and your desired width. You can also use the hide classes:
http://www.shape5.com/documentation/General/Miscellaneous/Responsive-Best-PracticesAlso, please post your questions in the support forum boards of the template you are using so we can address a specific template, not every template has the same layout and css. Please also provide a url if you need assistance in that new post.