Neck is too thick
Legs need to be wider at the ends.
Study rainbow's tail and mane.
Ears should be a bit longer.
I have no idea what went wrong but it looks bad…
Well, Lyra's front legs are a little short, and Twilight's front right leg looks a little misaligned (too far forward)
and Lyra's face actually doesn't look too bad. I would suggest studying the legs of real horses to get a feel for how their legs should be bending.