Can't see A1084 AirPort Express behind A1354 AirPort Extreme
I cannot comment your post, but at least I have a suggestion: Download a copy of Airport Utility 5.6 working with Mavericks here.

Edit: it seems to me your network is working as always (at least before you began fiddling...:-)), but the thing is you updated Airport Utility to the newest version and therefore cannot see the Expresses? This is a "feature" of the newest Airport Utility.