Okay, I'm gonna be that guy. The one that's all "YOU SEE THAT ONE LITTLE THING THERE YEAH IT RUINED EVERYTHING 0/10." And if I come out as rude, please don't be offended, I'm just really bad at choosing the right words. I'm gonna be going off the 2nd image. I'll name it 1 - 4 from left to right.
Also, since there's no lore or names, I'm going to have to go purely by poses.
1. She looks an awful lot like Pinkie Pie, and judging from the pose, acts(?) like her. We're talking original characters, not redesigns. And what's with the face design and insect wings? Normally I would assume it's because of a tribal back-story, but the logo says "Roommates" so, I don't really understand.
2. She looks pretty good, in my opinion. I'm not much of a fan of a solid-colored mane, though. I don't know how to explain it, but it doesn't look "right." I would suggest a different shade of yellow for a secondary mane color, but otherwise it's really good.
3. She is probably my favorite of the four. However, there are still a few flaws. The wings, again, need some sort of story to make sense. The mane, honestly, looks nice, but I think a navy/dark blue would be a better fit. Lastly, somewhat off topic, the cutie mark. What exactly is it? I know it's a panda, but it's too low-res for me to see.
4. Oh my god what is this creature This last one probably needs the most work. Let's start with the coat. It's a WAY too obnoxious color. Hot pink is probably one of the worse colors to pick for the coat, besides neon green or orange. The mane isn't much better. While I said I'm not a fan of solid colors, black and white isn't the best choice either. If you want to keep a pink color for the coat, I would suggest it be lighter, and the mane be... anything.
Overall. As I said twice already, it's hard to give advice without any personality, lore, or name (I will admit, though, it's hard coming up with them). Anybody giving suggestions are limited to poses and the cutie marks, which are extremely sensitive and can be interpreted differently than intended. So, I guess there's my list. In the time I typed this I could have gotten that school project done And if you need any vectoring done for them afterwards, send me a PM, because I have nothing better to do.