Thank you for writing.
The groups in the ribbon bar are StackLayoutPanels and they are designed to arrange the elements inside lined up horizontally or vertically. So, probably the easiest way to achieve the desired functionality is to use several groups that arrange the radio buttons in the desired order. In this forum thread
you can find solution for two groups that can easily be extended for 3 or 4 groups.
Alternatively, you can wrap the items in a WrapLayoutPanel and place this panel in the content holder of a single ribbon group. Please note the way the radio buttons are arranged in this panel will depend on how big in width they are.
I hope this helps.
All the best,
the Telerik team