.....you do everything together.
I love how they wait for each other to do things, ask for the other one, and dislike being apart. It reminds me of my siblings when we were little. You truly are best playmates! Even the quarrelling, and not wanting to share, you learn how to get along and work things out. These two are not capable of working it out themselves most of the time, lots of parental intervention needed still, but they'll get there :)