I think it's important to remember that this isn't a Joe Johnson for Rodney Rogers situation. Those are the types of trades that kill a franchise. Here, we'd be trading a young guy who projects as a role player (rather than a potential star like Johnson) for a legit chance at a championship (rather than no realistic shot, like with the Johnson trade).
I have no idea what to expect from Bradley. I like his potential, but have to defer to Danny. If he thinks he's worth moving, then I'd do it. It's the same thing with Semih. I really like Erden, but I'd say his ceiling is a good backup center. If we can trade him for a better shot at a championship, we've got to do it.
I would explore trades for guys like Parker and Butler based around second rounders and cash (along with Marquis' contract), but I wouldn't hesitate all that much if I had to trade one of the young guys for a decent backup.