Since her birth, Zayd and Zahra have maintained a medium-roast rivalry that I think we keep in check pretty well. It sometimes makes them both completely irrational but it also spurs a little healthy competition. From what I've heard, it's just part of being siblings. I don't remember rivaling with my brother but maybe I'm just too busy with the three chickadees to remember anything.
Since Z3 was born, we get lots of big kid rivalries over who Ziyan loves the most, who he's nicer to, who takes care of him more. You get it.
Lately, my littles want to argue over who is more my baby. To be fair, Ziyan wants to be a big kid every second of the day until Zahra notices I'm available to baby a Z and suddenly there they both are. Here they are arguing over who gets to sit in my lap. On this occasion, Zahra won. I figure middle children need a little extra loving sometimes. Let's hope this phase passes.