The family tree attached to your DNA results should only include ancestors you are definitely related to, not any that are related to you only by an adoption. As you're finding that can play havoc with the hints. All of those people in your match list are related to you in some way. Ancestry then compares the trees of all of your matches to your tree and when it finds matching people it creates a hint. But it's only a hint and doesn't mean that that's the way you are related to that match.