Have you ever worked for a family owned business where the family members also worked? I have, and the butting of heads is really something to behold. So much so, and usually over petty stuff, that it can make everyone uncomfortable.
It can be so childish, this situation, and watching siblings in a family owned business, adults mind you, argue like they are 6 years old is never good. Apparently that childhood rivalry takes a long time to evaporate in many cases. Then again there are situations where that is not the case, where everybody is pulling together lest they pull apart. Generally speaking they do better work, and are often more successful.