That's a great way to present harmony, with the lovely sisters, posing so confidently and closely, plus the combination of their crests above. It's like Luna's giving her sister a big hug. The princesses look terrific, and I'm amazed at how you got Celestia's symbol to have the layered effect with such subtle shadows. (Also, how much of a pain was it to line up all of the vector flame licks perfectly?)
Together the sisters shall rule, never to be parted by discord again. They are one... one in purpose and goals. Equestrian Principality, will stand for all time. The New Luna Republic will fail to tear apart Equestria, with Luna fighting on the side of her sister.