Another reason you had to separate Kentucky, Rean, and Roan into three teams was the Divine Sense Bending Skill. If they wanted to start capturing the Time Plates, they had to make sure no one was looking. In their group, only Rean, Roan, and Kentucky can use the Light Bending Skill since it requires Light Element.
As long as a Divine Sense touched their Bending Skill, they would know someone nearby was watching. Since the Time Plates were supposed to be impossible to take away, it would be too weird if everyone started to see the twins' group doing precisely that.
So, while avoiding the various other experts in the Future Realm, they also began to take the Time Plates into the Dimensional Realm. Of course, it was easier said than done. Even with the Divine Sense Bending, sometimes they would bump into someone who simply wasn't using it. Making sure no one was watching was a nightmare, but they were pulling it through.
One plate, ten plates, a hundred plates, a thousand...
