I've never bonded bunnies myself - but I do some work with shelters so I know a little about it
Well hopefully first off all your rabbits are fixed, because that can really reduce the amount of aggression they could show to one another.
Make sure the rabbits meet in a nuteral area - somewhere neither have been so that the one that's been there before doesn't see the other rabbit as invading his/her teratory. Some people put them in a bathtub or hallway like you said.
If they nip and mount each other - let them. They need to figure out who's boss bunny. If you just let them figure it out, they should stop the nipping and mounting. If you seperate them every time, then it will just start all over again next time they are together. Only seperate them if they are truely fighting.
If they seem to be getting along, let them stay together as much as possable when your around to supervise. They should eventually learn to be good friends.
I've heard of some people bringing the rabbits they are trying to bond into a slightly stressful situation, so they can bond together over that. For example, bring them all on a short car ride and they may huddle together for comfort and learn that the other bunny is a friend.
The most important thing is to just keep at it, eventually they should learn to tolerate each other, which will then turn into friendship. The more time you spend on this, the quicker you should succeed. Maybe at least 20 mins a day of them being together, provided their are no fights. If you want, get Ophelia and Penelope use to each other first, then bring in Oliver. If your most worried about Ophelia and Penelope then those might be the two you have to spend the most time working with. Make sure you watch them when you finally have all three together though, you don't want anyone to get ganged up on!
Good luck! Let me know how it goes!