Just some small insight, everypony depicts Luna as a younger sister yet they are TWIN sisters. It's nothing big but, i believe that Luna is only smaller because of her banishment, so when comics are made about Woona/Tia (what I like to call their filly forms) it always strikes me as odd that they would have such a drastic difference in height. Still a great picture just something I noticed.
I always figured they would have specified "twin sisters" in the pilot episode if that were the case, instead of calling them older and younger which suggests different ages to me (then again, I'm not a twin, but an older brother, so I'm biased!)
Leaving it vague does make for lots of nice flexibility in storytelling...
Yeah, I'm with you on that one. Whether or not siblings are twins is important enough to mention AT LEAST once, especially in a kid's show. Besides, cute and innocent little Woona + responsible big sister Celestia make an irresistibly cute combo!