All four of your OCs seem like they were specifically created for each other. Strangely enough, their chemistry together is based on contrast; they are polar opposites and yet require the other to be complete. The mutual dependency they have on each other does steal from their individuality, but they have good synergy when they are together. However, they pretty much always must be together.
Your characters are "dragon ponies" and assistances to those dragon ponies. I'm really not too sure how I feel about such a union, especially since nothing in the show suggests half-pony breeds of any sort. I'll have to give you the benefit of the doubt here, though, and assume such a breed is legitimate.
As characters themselves, I see nothing wrong with the material about them you provided, although I did note how brief your descriptions were. Of course, if this is exactly what you wanted to reveal about your characters at this point, I see nothing wrong with it.
Oh... you might want to proofread it a bit. "Additude" is not a real word.