Separating Facetime IDs on 2 iPads Thankswhile keeping one Apple ID

First I got my 9 yr old grandson an iPad last Xmas (I did not have one). I set it up with my Apple ID (I pay for his apps and keep an eye on what he does). But today I got my own iPad and tonight I am getting his Facetime friend calls. Is there a way to keep the Apple ID the same on both iPads, but have separate Facetime IDs? (And soon, his sister will get an iPad Mini and so I'll want 3 Facetime IDs with my having my Apple ID on both.

Thanks,

SusanD