As far as I understand you want to show all three tables records in same RadTreeView control. If this is so please explain how exactly you want to show that data in one RadTreeView. The regions will be the root nodes, all sub-regions will be added as child nodes for each associated region node. In this case at which level in the RadTreeView hierarchy do you want to add the engineers and how you want to link them to the regions? A sample structure with couple of regions, sub regions and engineers data will be very helpful.
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to the blog feed