I think you would have special dynamics even if the 3 were sisters. Each would likely have its own, unique personality.
Right now, Barred Rocks and Black Australorps make up my little flock but I've almost always had only one breed of hens at a time. When I had roosters and since I wasn't breeding them, the rooster was an excuse to have a bird that was just for "looks." Since roos are roos and hens are hens - I've really almost no experience mixing breeds.
By your question, I suspect that you already want a variety to enjoy in your backyard. Mixing breeds is quite common but I think it would be a kick to have only one physical difference between the hens.
Next year, I may get Barred, White, and Buff Plymouth Rock chicks. Since I've only had the Barred a couple of times and never the Whites or Buffs, I'm a little concerned that there may be too great a difference in size and even body shape; the White Rock is commonly used in meat crosses and the others aren't. Before committing to these choices, I'll be sure to run this idea past the BYC community.
If the Australorp came in as many color variations as their relatives, the Orpingtons, I'd be very pleased . . .
Steve
Oh, my BR's are larger and boss the BA's, but they've lived their entire short lives together and get along just fine.