Well... you know that I have my two.. Ralph and Ruby, and then I fostered this local bun, Buzz, who is currently on rabbit rehome? WELL... Ralph and Ruby are now successfully bonded, BUT if Ralph gets a whiff of Buzz around the house or on toys outside, then he will chase and bite Ruby and the bond goes a bit scewy for a little while. When I remove anything that could possibly have the smell of Buzz on it, Ralph returns to normal, but it takes a couple of hours/days for Ruby to trust him again. I now have to be really careful what toys/items I share between the single bun and the bonded pair, because the smell of Buzz really upsets their bond.
Obviously I'm a bonding beginner, so I'm not particularly experienced in bonding three, but I'd probably say that a four is better. Although, you haven't yet bonded Sooty and Oreo, so maybe if they're all introduced to each other at the same time it will be different?
Also remember that there are people at Rescues who can help you. That was my fall back option if my bonding Ralph and Ruby didn't work.