I often felt like the younger one got the short end of the stick, since I was always dragging her to DC1's various events.
^ I felt this way. There are things you can do to change this. Just weighing-in. I'm an adult with a 7, 9 & 11 year age difference from my siblings. At least when older teens are still at home -- make them attend some of the younger one's activities. Cheer-on the young child at their sporting event. Go to their school play. The older ones need to have an idea of who the younger one's friend are, their activities. It all adds-up to knowing them.
The older ones don't just get to be admired