I don't think they should have been treated disrespectfully at an MTV award dinner or any other function for that matter. They are young women who happen to be the daughters of a candidate in a very heated political race. They are probably not fully familiar with their father's legislation and political career, and were asked or recruited to come and say some nice things about dad. The reaction of the audience just shows how far as a society we've fallen from the days when people could act in a civil and courteous manner. They're just kids caught in the crossfire, and the audience's reaction just smacks of very bad taste.
I don't think it was a disrespect to boo them. In that forum, if you agree with the message you are supposed to show enthusiasm. If you disagree with the message you show displeasure by booing. It's part of the territory, and that they are not familiar with their fathers policies doesn't wash.
If they are not familiar with their fathers policies they should not make a political statement. If they do, they open themselves up for this.