Dog Agility Confidence Building Game
Gisela Griesser demonstrates the game called Cardboard Chaos from Absolute Dogs in the UK.
You want to be sure your obstacle course is challenging but safe. No sharp edges or things they can get easily caught in.
For more timid dogs start with just one low box and add to that as they gain more confidence.
And while Gisela used her dogs breakfast kibble, you may need to start with higher value rewards if your dog is timid.
Letting multiple dogs work the course at the same time will build confidence as objects move around each of the dogs, just make sure it stays structured and never leave any of your dogs on the obstacles unattended.