two iPhones registered on one iCloud id

i had an iPhone 5 which i gave to my partner and upgraded a 6+. i have now upgraded my iMac.

A] In Find My iPhone it only registers my iPhone 5 ( i have been unable to register the 6+ even though all the settings in the phone have been observed)

I read on another forum that only one iPhone is able to be tracked and it is tracking the 5 which my partner is using!

B) I am trying to set up face time and iMessages on my new mac but will only allow by using the iPhone 5 number.

I particularly want to have both phones locatable via find my iPhone can anyone help?