Try separating your characters (drag a portrait to the right to break the chain with other portraits). Leave the one who stole downstairs and only approach with the other. You can try a companion, as well, but they can only trade with him, not advance any quests.
Try going back later. If he at least doesn't immediately attack, you can talk to him and bribe him to like you more.
You can also revert to an earlier save / quicksave / autosave.