It looks like Pipp, Misty, Sunny, Zipp, Melody, and Izzy are getting approached by Storming Dust, Moonracer, and Chromia in a not so good way all while having those forced smiles by the pony that took away their talent (Not Starlight Glimmer, this takes place centuries after Season 9 of MLP, it's somepony else). The girls are rather threatened by this, and they're already about to huddle each other and back into a corner, but that's not what will happen. Instead, it will be a much more friendlier encounter and possibly the three telling them how much they miss them and that they need help, wanting their cutie marks back most of all.

As for why Misty is there? In my AU, she will eventually be friends with the mane 5 and my O.C. Melody Heartsong, but there will not be a sixth member, sorry. Instead, I plan on having Sprout, Misty, and my O.C. Melody become very good friends with the main characters. And what happened to the three other ponies in the picture, some creature rediscovered an spell that removes cutie marks and replaces them with an equal sign, basically removing one's talent and some of the magic. When ponies don't have their talent, they're basically like zombies and whenever they try to engage in what they specialize in, they can't do it at all really, this was implied in the Season 5 episode of Friendship Is Magic where Starlight Glimmer took away the ponies talents and made the village a dictatorship, giving the ponies false hopes.

Hitch and Sparky did accompany them, they're probably not in the castle.