How do you stop cat sisters from fighting?

Ugh!  My girls keep waking me up every night, or shall I say, the early morning hours.  I don't know who starts the drama (they are sisters) but I hear hissing then loud cat screaming and chasing.

Ideas to stop the fighting:

• Change the environment so the cats can have more of their own space.
• Put water and food in different places so they can have their own space when they eat.
• One litter box per cat, plus one more, and put them in different, out-of-the-way places.
• Try using a feline-appeasing pheromone spray or plug-in diffuser.