Overall, they're good general coverage cosplay event photos.
Some of the basics:
1.Busy backgrounds distract from the subjects.
Try to go to a higher f-stop and longer angles. They will blur the background (make the dept of field shallower) separating the subjects from what's in the background.
2. (Mainly for pairs and groups) Get the cosplayers to play to each other rather than to the camera.
This will avoid the "picture-day-in-the-4th-grade" look and feel to the photos.
This isn't a hard and fast rule. If you're going for portraits, then that look is fine, but the framing of the shot has to change to compensate.
3. Remember the "rule of thirds"
4. Try to avoid cutting off body parts.
I know that in con shots things tend to be rushed, but with practice, this will become instinctive.
5. Avoid bright sunlight if possible.
This will reduce shadows and high contrast, sunlight.
A fill flash can help, but still overpowering the sun is a huge task. Managing light is an art form by itself.
Manual settings are your friend. They make the difference between ok photos and great ones.
You're doing well. It's just a matter of more practice. The more you do, the better you become.
Good luck, and HAVE FUN!