James Young is the most intriguing to me, but no one is untrade-able. Oly and Sully are limited athletically and have a finite ceiling both are porous defenders. Smart can't shoot that well. Young needs to work on his D. I think that Smart can learn how to shoot, he would be my second keeper. Young has all the tools to play D, just needs to learn it so he would be my first keeper. KO and Sully have bench bigs written all over them.
Even if Sully got in shape, his vertical and foot-speed would only be marginally better. KO is plagued by the same kind of problems. These guys can play and are not without skills but I doubt they will ever be elite given their limitations at least not on both ends of the court. Guys will always be able to drive on them and beat them up and down the court.
Everyone else is expendable. Crowder would be nice if he is cheap to keep as an energy guy.
That being said we have no one that will get us a top tier talent. I would not trade Durant or the like for any of these guys or all four of them. Get real, even four number ones and these four would not do it. Thinking they would be a joke. You'd have to have the number one pick, 2-3 of these guys and another first.