SJL what a horrible situation. You are an awesome person for adopting your daughter and they are wrong with everything they have said. I would be very angry too if I was in your position. I don't really know what to say but I would be making it clear to them that if they can not accept your daughter and treat her with as much respect as anyone else in the family then you can't afford to have them in your life. I'm so sad for how it might make your daughter feel to be treated that way, even if it doesn't seem obvious she can probably pick up on it. I don't know what is wrong with some people.
Sorry, I haven't been much help! to you.