In the PON community, coping with PON sibling rivalry, which may include aggression, is a an experience that most owners experience sooner or later.

Canine trainers tend to point out the problem as being  instinctive and although a range of issues may complicate the situation, when it comes down to it,  some type of leadership and control is necessary.

Canines are social animals, they have rules that dictate how they behave around each other. Left to themselves, most dogs easily slip into their roles. Rivalry erupts when they disagree about their place in the pack or family unit. Although there are no guarantees, bringing together dogs with too many similar characteristics - same sex, same age, same breed (brothers from the same litter for example) -may spark serious conflict. So many commonalties make it difficult to settle who is top PON. Hormonal surges also have an effect. Possibly the cause is redirected or frustration aggression - attacking one's fellow PON or owner when agitated about a guest's arrival, is more common than one would imagine.
 

Can owners trigger rivalry ?

Often, owners can inadvertently trigger sibling rivalry by disturbing the hierarchical balance and rushing to protect one PON  from being "bullied" or granting him liberties, such as being petted first, which your alpha PON may consider his inherit right. The low PON on the totem pole now feels bold enough to challenge the other. Owners need to understand that dogs have their own set of social rules, whereas most dog owners want democracy, dogs don't understand a truly democratic concept".
 

How to cope with sibling rivalry at home:

Prevention, of course, is the best course of action. It's vital for puppies to socialize with other dogs - for example in puppy socialization classes or in the park. This way, they learn the unspoken but strict rules of canine society.

Exercise also works wonders and obedience training is usually a necessity. After the dogs have been together a while and are getting along, an insignificant scuffle or two might erupt. In theory, all dogs should be able to work it out together as long as the owners don't interfere. Owners must heed mounting tensions. As soon as you detect signs of trouble that you're uncomfortable with, take steps, don't wait for fights to happen because that changes the dynamics considerably." Often the problem can be relieved if, instead of protecting the perceived underdog the owner supports the hierarchy. Determine which is the more dominant PON and reinforce that position by feeding, greeting or letting the top dog out first. Usually this will help, but not always. "The problem with that approach is that it's often difficult to tell who should be the lead PON. "Secondly, it's really difficult for owners to play favorites with their PONS. When all is said and done, sibling rivalries usually can be resolved, but not always. Sometimes you're unwilling or unable to implement the necessary changes; or genetics or socialization shortcomings are intractable. If that's the case, the best solution may be to find another home for one of the PONS.