Hi Ryan,
Thank you for using Syncfusion Products,
Query#1:My problem is I also have 2 documents and neither of them are being displayed and I don't know why at all.
To have the document children in the DockingManager, we need to set the UseDocumentContainer property as True.
Query#2: I want the headers to have a template of icon checkbox and textblock which I can achieve however when I try to have the item expanded it doesn't work and I got no Icon to be allowed to expand.
We have edited the template of Treeview by adding CheckBox and TextBox in the TreeView Header which is in the Input DockingChild of your sample. Similarly you can edit the header of TreeviewItems. Please download the modified sample from the following location:
Sample:
CS_79de6969_ModifiedRegards,
Marimuthu S.