C#, WPF - grouping textblocks and text boxes

If a user selects among 2 systems, and 1 system has a list of text blocks and text boxes for 'Text Message #1' .... 'Text Message #5'. The second has up to 'Text Message #16'. I have defined the first 5 (for the first system). What I want to do is to group the Text Blocks and Text Boxes so that I can add the 11 other Blocks and Boxes should the user select system #2.

What's the best way to group these together in a limited space (the 5 are fine, 16 will require a scrolling box)? And, the best way to add Text Blocks and Boxes into the group when the user selects the 2nd system?