2nd iPad not showing up

I purchased a second iPad a few weeks ago. The first one is on its way to Gazzelle. I forgot to erase the first one. I've set the find my iphone to erase the device. I noticed the new iPad (with the same name) is not showing up on the find my iphone screen. It is connected to the wi-fi and all of the settings are selected in the device itself. Any tips?

Of course, I just noticed that the discussion option does not include the new ipad as on my registered devices list. Does it make a difference that the iCloud account on the device (new iPad) is setup in my wife's name even though my account is on the device and "on" for the find my iphone feature?

How do I register the device to my account and have my wife's account as the default iCloud account?