Still have a year left on my next plan BUT want new iPhone 6sPlus

I need help making a decision...

My husband and I purchased our iPhone 6 pluses last Dec./Jan. Our next upgrade isn't until June since we did the next 18 (we should have done the 12...) Anyways what I would like to do is get two NEW 6s pluses through Apples program so I'm guaranteed a new phone every year. Could I theoretically keep paying for our AT&T NEXT 6 Pluses since I can't cancel my next and I don't want to pay it off so my son can use them as an iPod and just keep them after I have paid my 24 installments and use the new iPhones BOUGHT with APPLES new financing with our current phone/data plans?

Yes, I know I will be paying double for a year since I owe still on those 2 iPhone 6 and will now owe Apple for the two new iPhone 6s but will this affect my mobile share plan at all?

I have our phones already reserved to pick-up at store but want to use the time between now and the 25th to make sure I won't be charged some hidden fee somewhere or if I'm required to activate a new line for the two new phones...

I hope I'm not too confusing!!!!

Thank you in advance!!!!!