In Sam and Dean's case, I wouldn't call being able to host angels a supernatural power. Sam's demon blood thing is much closer, and Dean can't do that.
Honestly no one really understands whether Yukio is jealous of Rin's flames or not, on top of all of his other jealousy issues. Okay, well I've done some thinking and he might be (or he might not be). He did say if he had them he'd go crazy....but call me silly, but I think after that is when he'd piece himself back together.
The whole uniqueness thing can be solved by giving Yukio different powers. Less offensive, or perhaps more long-range ones. Yet equally deadly. Personally, since they're brothers I think both should inherit things from their "father". And Yukio will be left with nothing and revert to his "protected little bro" status when Rin catches up to him in sword skill, and they face more enemies humans can't handle. I don't like that, and I don't think Yukio would like it either.
Izumo doesn't have powers, and she admitted that demon blooded people were common in the order. We haven't seen the last of them.