It may not ever happen. My brother and I never got along growing up, even though we were very close in age. We were just different people, and I have learned to accept that. Now that we are adults, we tolerate each other's company to a point, but seldom see each other. Sometimes it just doesn't happen, and trust me, there is nothing the parent can do to influence whether or not two people (even their children) get along. It's all about personality and interest; who they are as a person, and try as you might, a parent has no control over who their children are as people.