My Luna is kind of like that too, she barely tolerates us loving on Izzy and has snapped at her a couple of times defending "her" Daddy's arms. We got Izzy when Luna was 5 months old, and Izzy was 7 months old, so they've pretty much grown up together as well. Izzy just turned 6 and Luna will be 6 at the end of the month. We've also decided no more babies here too, but we're okay with that

Two is my limit I think, anyway