In Watchtower theological theory, the JWs living in the New System will get along because they will not have Satan pestering them, the worldly influences will be gone, and Jehovah's spirit will flow freely, strongly influencing JWs to bahave themselves.
In reality, if you took a bunch of JWs and put them on an Island all to themselves, where Satan didn't know about it, and Jehovah's spirit flowed freely, if they got along any better, it would be because of the tight controls exercised over them.
However, it is all nonsense. Just look at the freedom that ex-JWs have gained, and the experiences we share - yet even we cannot seem to get along all the time. I doubt that even perfect people could get along ... otherwise we would simply fail to be truly human.