A full factory default reset is difficult to do, since you almost need to have 3 hands to do it properly.
Try a "hard reset" as follows:
Power up an AirPort Express for a few minutes
Hold in the reset button on the back of the Express for 8-10 seconds and release
Allow a full minute for the Express to restart to a slow, blinking amber light
On the iPad home screen, tap Settings
Tap WiFi
Look carefully for a heading of Set Up a New AirPort Base Station
Tap on AirPort Express just below that heading
If the Express is operating correctly, the utility will see it and walk you through the setup
If you continue to have difficulty after you try this several times, I would suggest that you take the AirPort Express devices to an Apple Store....if you have one near you....or contact Apple Support directly for more assistance.