My girls are from the same litter and they were bonded from birth...the breeder said they slept, played and ate together from the very first day...they even move the same! First I thought it was a ploy to get me to take 2 but it wasn't....their bond is obvious and amazing!
They are now 4 1/2 and were spayed at 2 1/2.....they've never had a fight or even a little disagreement and we had no trouble training them.
I know not everyone has the same experience we've had but.....I wouldn't have it any other way