All four of mine get along quite well, and I also think it was due to a lot of deliberate actions on our parts over many years. We pretty much have always required the kids to be nice to each other. We don't tolerate rudeness, name calling, physical fighting, or put-downs. I cringe when I see those t-shirts that say things like "brother for sale." It's not like we talk to our kids about this all the time- it's just been that way for a long time. If we hear an occasional sarcastic comment, we'll pull them aside and ask, "how do you think that made your brother feel?" Or say, "I think your sister was hurt by that comment; I would have been." We don't do the "you must come to every game or piano recital or art show" by your sibing, but we do expect them to be supportive. We also are very much into the "life isn't fair," philosophy, so we make sure they realize that sometimes one child needs attention and sometimes another child needs a new something, and we aren't going to do the same for every kid just because (impossible with four anyways) and I actually think that cuts down on the jealousy. Our kids are fairly different, but it probably helps that the two older ones are both girls and two younger ones both boys (each gender set two years apart). I will say, though, that even the older and younger ones get along quite well. Ds10 just learned his first song on the violin and immediately wanted to call up dd20 at college to play it for her. She was appropriately "wowed," as required.
I didn't and don't get along nearly as well with my siblings, although I get along best with the one who left our dysfunctional family early on, as I did (the other three stayed fairly close to our hometown). In my mind, mom and dad set the stage for sibling relationships and dh and I were really committed to modeling healthy relationships and guiding them.
