Let those added to the lair also be able to add others. The master of the lair isn't always around.
Maybe a DM can wand two masters of the lair so they both can add others?
I am almost 100% sure that it isn't possible to wand two "admin" PCs.
To be clear, "master" is the flag for any lair owner flagged so by the administrating PC.
The admin has only two unique powers that I've found - destroying/building a new lair and adding PCs as masters of the lair.