It varies. I had five sisters, and the ages were spread out in places. As a general rule of thumb, I'd say hellish until you're all in your late teens. Then, depending on whether you get along or not, it's like having live-in best friends.
Then you can have it, for a bit. Not to fluster you further, but it's only a matter of time before Peter has a fit and comes looking to bring you back home, even with my telling him to stay put; and we know it. I'd rather be there to run him off and help you keep calm when that happens.
It does tend to keep one preoccupied. Remind me to put an oxygen tank under the front desk.