That looks like a tough space, but perhaps wall mounted on one side and on stands on the other?

Or, since you have your LCR mounted high (and I assume angled down?) the surround could also be mounted on the downward ceiling slope and angled at the listening positions.

While far from ideal placement - but really only a few have those options unless building from an unfinished room - you could then adjust levels of the channels to be balanced in terms of output.