1 - Straighten it out and crop in on the left and right. The dark area on the right and the lines on the left are a bit distracting. Otherwise, I like it.
2 - Good shot, though I wonder if it might work better if she was looking at you.
3 - Excellent shot. I'd like to see more room on the left and right and then the whole thing shifted down a bit to show more of the archway at the top and less of the brick at the bottom. The contrast seems a bit high (I'm looking at the face of the cosplayer on the right which seems a bit overexposed). It's always difficult to deal with black outfits and light backgrounds and to expose for both well. Overall, very good.
4 - The panty shot isn't a huge deal as it's not suggestive or gratuitous, and you can easily hide it. You don't want them posing directly behind each other. The person in the back and be a step to the left or right and make a much more interesting shot. Also, you don't want to shoot it too wide/close, otherwise the person in the back looks much smaller relative to the person in front...unless that's what you're going for. Have both people looking at you, or at each other, or away in the same direction. As is, it looks like one person was looking at one camera and the other was looking at another photographer.
5 - Nice shot overall. I don't like the cropped off arm. I'd suggest cloning out the sprinkler head right above his head.
Thanks for sharing and hope to see more!