Judging from the source, the references are as follows:
Sweetie Belle: Shampoo from Ranma 1/2 (Anime)
Apple Bloom: Momoko Akatsutsumi/Hyper Blossom from Powerpuff Girls Z (Anime)
Babs Seed: Catra from She-Ra and the Princesses of Power (Netflix)
The rest seem to be originals, but I think Scootaloo’s dress is based on the one she wore in the first movie.
@Background Pony #A344
The costumes they’re wearing all seem to be referencing other cartoons. Babs is wearing one worn by Catra in the Netflix She-Ra series.