And just to round out my sibling story I grew up with my older brother and my younger sister. After a divorce and the addition of step families on either side I am up to a total of three brothers and three sisters. It is a wonderful, blended family and although I am only close with half of my siblings, I only have one that I prefer to not claim.
Actually, though I grew up in the same home as my mentally ill brother, my parents also divorced and my dad remarried. So I also have a step brother, step sister and half brother. They were all a net positive in my life. But my full-brother caused a lot of stress for my dad's second family too, so my relationship with them really only had a chance to blossom once he stopped visiting. My step-brother had his own problems that he eventually outgrew - so I'm sure it wasn't all roses over there. I continue to have a close, but geographically distant relationship with my step siblings (my half brother is much younger, so we're friendly, but not close).
When my father died, we did really come together as a support system. Minus my brother, who had started stealing from the house and having tantrums about what he was "owed". I guess it just illustrates what a crapshoot family can be. ;)