for the green bridge, you should have one base support and two supports on the roof of the bridge. Right have them connected horizontally. In order for the bridge to support the dual tracks, all you have to do is switch the panels from horizontal to vertical. I did some digging, I don't have the complete set of a bridge to show you how it is done. Hopefully you will find photos online to help you.
My Trackmaster/Tomy/Plarail Photo Gallery Page (over 600+ photos and still under construction)
https://www.flickr.com/photos/183311600@N03/
https://www.flickr.com/photos/183311600@N03/