Very nice tank! the girls look lovely. Girls are fine together as long as there are lots of hidung places, and enough girls so they can spread their aggression out.
However, as was said, the plec needs a bigger home. I don't know if you have a bigger tank lined up for him, but if not I'd try to return him to where you got him from.
Usually the girls will sort out their conflicts, if as was said there is enough room, hidy places, and girls. It is good to watch the to make sure they settle in together. Occassionally one just won't fit.