I found the solution. Convert Callback to DBLClick.vi from the VI.LIB has a parameter Return Meet Filter Selection, if this is set to TRUE, I get the behavior I was looking for. The parent folder will expand on a double click, and the root channels can only be selected.
Here are the code solutions to the 2 issues that were discussed. Thanks for all the support.
This is the code for the Custom Filter.
This is the Code for the double click event.