Hiya
Yes Chickens can be rotten to each other - pecking orders are dreadful things.
Can't tell you how long it will last, but if it goes on for more than three days, I would
be tempted to take the bullys out, put them in a dark box on their own for a day or two, then put them back in, it usually sorts them out.
Good Luck - it is normal, but not nice to watch