L., First, Congradulations on # 3.
I was 18 when my mom had my third brother. Even though I was older, I felt "jealous" of the baby. I wanted all the attention, that he was getting. After I had my second son, and then four years later, was having my third son, my oldest was acting just like I was. I did what my mom did, to me. I would set aside the time we had together, and play, do homework, watch a movie, or even talked. My mom would take walks, with my third brother, in the stroller, and we would go together, and just talk. I started to do that, and they loved the idea of pushing brother in the stroller.
I would make doctor appointments while my two older sons, were in school. That made it so much easier with handleing the doctor appointments with just one.
On the weekends, as soon as it was nap time, they knew it was time for their time. The oldest would pick out a game, or a book, and we would read or play together. I would let the oldest one pick one day, and the middle one the next.
When I had my Girl (#4) I was able to show my youngest boy how to be a big brother. He was the only one home at the time. They all love each other, now. I would never change the way I helped them cope with a new sibling.