Another way to portray how Fluttershy's brother might be portrayed in Season 6 is described in this post.
Fluttershy is older than her brother. "Flutterbro" was still a young foal when Fluttershy moved with Rainbow Dash from Cloudsdale to Ponyville. When Fluttershy's parents divorce in an upcoming season 6 episode, her brother is now a teenage pony who have rarely seen Equestria outside of Clousdale, being a Pegasus.
Still a few years away from adulthood, it is agreed that Fluttershy should become her brother's legal guardian until he becomes an adult.
However, he still has to learn about life outside Cloudsdale (e.g. on solid ground).
Flutterbro's closest friends living in Ponyville are Rainbow Dash (they knew each other when Dash still lived in Cloudsdale), Discord (Flutterbro and the dracoequus share a fondness for mischief), Derpy (Flutterbro sees her as potential girlfriend), and Big McIntosh (Flutterbro sees Big Mac as a potential friend).
Flutterbro gets along fairly well with Applejack, but regards Rarity as "too girlish" and Pinkie Pie as "too childish". He respects Twilight Sparkle (mainly because she is an Alicorn princess). He is sometimes annoyed by his older sister because Fluttershy often has him doing chores involving taking care of her animals (which Flutterbro finds tedious and boring).
Flutterbro gets along fairly well with Apple Bloom, Sweetie Belle, and Scootaloo, considering himself something like a big brother to the Cutie Mark Crusaders.