The first thing I would do is enlarge the run if you can, and if at all possible, add some hiding places and things like roosts and boxes, as others have suggested. Next, it is normal for chickens to squabble a bit when deciding who gets to sleep where, and it is normal for them to compete for the highest roost. If possible, I would make all the roosts the same height. If your nest boxes take up any of the floor space in the coop, the next thing I would do is raise them enough so they have that much more floor space to walk in. Your coop is small, yes, but unless they spend much of their day in there, I am not sure that is your biggest problem. If they actually have the full 2.7 sq ft available to walk in, that is. If food and water are in the coop, perhaps you could set up a small protected area in the pen for them to free up some more floor space. A "covered front porch" might help, too; depends on the setup, of course.
Another thought -- if you live where winters are bad enough that they stay indoors some days, this can really make them feel crowded.
When you have one bully, or one who is worse than the others, sometimes you can solve the problem by putting the bully in "chicken jail" for several days or a week. When they rejoin the flock they are at the lowest point in the pecking order. You might have to buy a dog cage or the like to do this. I've read it's best if they can see each other during this time.
Actually, if your Wyandottes are as bad as mine were, they may be the biggest problem. It may be that your whole problem would be solved by rehoming them. I know you don't really want to do this, though.
Good luck!