Derpy had followed Rainbow Dash to Sugar Cube Corner the day the latter disappeared. She didn’t put much thought into it, but soon started to notice her other friends slowly disappearing. Being sneaky, she entered the bakery at night, and found a trap door in her investigation.

However, Pinkie found her snooping, and Derpy came up with the excuse that she wants to learn to bake too, so Pinkie took her in.

First part to this ask:

I have! I’ve only done the sisters at the moment, but I’m going to work on the rest soon ^^

I’ll also fill out a quick summary of them soon enough but basically

Limestone and Marble Pie came across Pinkie during a harvest, and while Limestone was curious how she managed to kill a full grown pony, Marble was more horrified, and in fear for her own safety she did her best to not anger Pinkie and ask about her ‘hobbies’ to make it seem she was just as interested as Limestone.

They’re living their best lives.

They begin to notice how worse Apple Bloom seems to be getting, but she won’t tell them what’s wrong (out of fear for hers and their safety) So they start inviting her out more and more to get her to cheer up and help her out.