It looks to like Amir takes games off. Games where he's just doesn't show up. He may be running on fumes. He'd be best coming off the bench.
Zeller has value on offense, but is strictly a second line player on the defensive end. He's getting minuted now because of the injury of Horford, and the C's shortage of quality bigs. Again he should be a second line bench player.
I also agree KO and Horford should be starting. Kelly may not be very athletic, but he now understands how to defend by good positioning, and being 7 feet helps. He rebounds at least as well as Amir, and has much better shooting and play making skills.