Really nice picture but I don't see here this so called "Twilestia". It's just relationship like between mother and daughter, nothing more. Tia simply wanted to relax and have some fun with her favourite student, trying to push Luna into more social life(and failing at it, since Luna looks not amused with Twi/Celestia sheneningans)
I really love this. As a TiaTwi fan. It just seems perfect for them. Luna just feels like a third wheel. Like, why did they even drag me along.
I think that Tia dragged her along so that if seen it would not draw so much attention if just her and Twi. So to keep there little relationship a bit more secret from the public. After all Tia is the ruler. So she has to be careful so as to not cause to many problems for Twi.
This makes me giggle uncontrollably, just like Twilight Sparkle in the picture. It's so much fun to see the elder princess being so playful with her Most Faithful Student at what should be a formal event. But what then strikes is Luna's expression: at first it looks a bit like exasperation as the two make fun, but then I look more closely at her eyes and see sadness. Is she sad because she feels disconnected already and now she's too self-conscious, or guilty, to appreciate the fun? Or even join in? (Or maybe I'm just reading way too much into it. )
Even if there are some technical issues, I'll leave it to the experienced artists to chime in on those. It's an adorable and very thoughtful painting.