Problems installing a second booster: WN1000RP

Bingo!  After disconnecting #1 and setting up #2 per the manual's instructions via WPS, both extenders are showing up in Attached Devices (where neither was there before, mysteriously) and appear to be working.  They have the same SSID but discrete IP addresses.  The USERNAME_EXT is the only one that shows up in my iPhone's list of available wifi networks but I guess I was mistaken to expect this to be any different with two extenders.  Having found the devices via my browser as you suggested, I took the opportunity to update their firmware and that went smoothly.  I also updated my router's fiirmware via the router interface.  Both devices now show CONNECTED but one reports 54 mbps link rate and the other 11 mbps.

Thank you for your patience and expertise.

This is a fairly technical process for the average homeowner with a wifi network  I can imagine that the various interfaces, the passwords for router, wifi and service provider and the tech protocols may be too much for most people to master by themselves.  I managed because I am reasonably competent around computers and because you were so helpful.  There must be plenty of people who are floundering though; I mean, how often would they even think to update firmware, or know how to?  I am very grateful for your assistance.