creating multiple family accounts

I am sure this has been asked in this forum, but I am not able to find this exact situation....

Our Family has an iMac that is the "parent' for our single itunes and icloud account.....We also have 3 iPads 2 and 3 iPhones 4 - this single account is used to buy content and back up all of our "child" devices, etc....

Problem:

Both my wife and I travel frequently and we want to use Facetime to visit with our 2 children whilst away The way things work now, it seems that all imessage and facetime activity is shared amoungst all devices, all the time... the wife and I would like to insulate the kids ipads from our conversations - how do I easily do this?

Do I need to set up separate itune accounts for each of us?

Is there a way to manage all itunes purchases from my "master account" but have the separate itunes account so that the facetime app is controlled and not sharing everything amoungst all devices?

Thanks in advance

RTHD