I traded OG Vanilla and a Backyard for DBH back in the summer so you should have no problem with the beers you listed above.
Yes, you could land one with your FT. However, personally, I would keep the assassin and the vanilla. Had dbh about 2 weeks ago and it isn't the same anymore. Hardly any rum flavor and the peppers were faint. Dbh is my favorite beer of all time but that is only when it was fresh. I wouldn't trade for it now. Just my .02.
No idea. It wasn't my bottle. Don't get me wrong it was still a great beer. It just wasn't as good as it used to be.