You shouldn't be using multiple ObjectTrackers as that is not supported at the moment, but rather have a single ObjectTracker with a .wto file that contains all three objects. You can then add three ObjectTrackables as children to that single ObjectTracker and for each trackable you can specify with which target it is associated and what augmentation it should have.
Please let me know if that works for you, or if something is still not clear.
Everything works now, thank you. Can you tell me is there a limit of ObjectTrackables to the single ObjectTracker?
I'm glad to hear that everything is fine now. There is no limit to how many Trackables you can have on a Tracker.