I assume that it's one AT4 per TV that you want to watch stuff on. I haven't found a thread yet that talks about using one AT4 but getting the programs from the apps onto multiple TVs. If there is a way... How?
I'm sort of in the same position, I was using an ATV3 but have since purchased an ATV4 so that's in the lounge, my ATV3 will go in the bedroom and I'm gonna get 2 more ATV3's which will probably be second hand as they can be picked up fairly cheaply now for the kids rooms so then we all get to use my iTunes purchases as well as Netflix etc.
I gave the ATV2 to my mom, my daughter has an ATV3, and our old ATV3 sat in a box waiting for a relative who wanted one. The ATV4 had issues with wi-fi so it's currently in the shop getting looked at, I'm pretty happy I hung on to that second ATV3.