I've turned everything off except for the Extreme.
Power off all the AirPorts for a few minutes.
Then, power up the AirPort Extreme first, and let it run a few minutes.
Power up one Express next, and get it working correctly. You get the idea.
You are probably losing 40-50% of the wireless signal strength if AirPort Extreme in Closet really is in a closet, since a typical wall aborbs about 10-15% of the signal and you likely have 4 walls in the closest.
You may need to move the AirPort Express devices closer to the AirPort Extreme so that they will pick up a stronger signal and maintain the Extended Network setup.