Shutter speed can be a factor if it's long enough to allow location lighting to be captured by the image. Ideally, you want to have enough power in your strobes to completely negate the room light (i.e. your photos would look the same if the room lights were on or off).
What strobes are you using?
Shutter speed does not factor in your strobe light exposure as long as it's under the sync speed, so the strobe lighting will look the same at 1/250 or 1/60 ... but the slower your shutter is, the more room light will creep into your image, which can induce soft edges and discoloration. This is why setting shutter speed to the max sync (usually 1/250) is generally recommended.
While we're on the topic of the strobes, I agree with what has been noted above in that you didn't fill the entire frame with light for the team photo. The whole left side looks dark. Ideally, with a two light setup, the left and right lights will be balanced in power so you have even lighting across the whole group. For the cheer leaders shot, it looks like the strobes are aimed so that most of your light is being "wasted" falling in front of the group on the floor that you're cropping out of the photo, rather than being directed primarily onto your subjects.
17mm is a very wide angle for portrait work. Clearly in the gym you would have had plenty of room to move back to use a longer lens. I would recommend taking test photos at f8-f11 with all of your lenses, using different zoom values, using a tripod to find out which of your lenses provides the sharpest images. I'm guessing that your 50mm will likely serve you best at those f-stop values.
Here's an example of one of my own shots, f19, 1/250, ISO500, 28mm (using a 24-70mm f2.8L lens)
Hope this helps.
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