Stacy had to go because her social game was atrocious. She clearly hadn't really bonded with anyone and was treating everyone like shit (as evidenced by her reactions to Coach & Edna). Keeping her around would hurt tribe moral and she'd have every reason to flip once the merge came along.
As for Brandon, he's up there with Albert for the title of strongest male on his tribe. He's causing problems, but he clearly plans on being loyal to the alliance of five, so as long as the crazy can be dialed down, he's worth keeping.
So, weak Edna is probably on the chopping block for her tribe while Mikayla has no alliances either. One of those will be next to go if they lose.
On the other tribe, I think shit's probably going to hit the fan real soon. It'll be either Elyse or Ozzy getting the chop, surely. And it will cause so much drama.
People that clearly don't win this season based on their edit: Albert, Elyse, Keith, Rick and Whitney. We've seen very little of them in the first four episodes, almost none in fact. Also, Ozzy's edit is extremely negative and meant to make him look like an idiot at every turn (especially in contrast to Coach). So we can rule him out as well. I'd also rule out the three girls that look like the next to go (Mikayla, Edna and Elyse).
The contenders would then seem to be Brandon, Coach, Cochran, Dawn, Jim and Sophie. Very entertaining bunch if you ask me.
Only people I failed to mention are the two on Redemption Island. If it's like last season, they'd need to win the next four challenges in a row to return. Not going to happen.