I'm guessing you guys probably don't know your control keys. "Enter" only works for selecting main menu options, if you want to select things in other places, you'll need to use the "jump" key for confirmations and "attack" key for cancellations.
To find out and change your control settings, go here:
(The highlighted option)
And then change the control keys as you like, I labeled the commands, in case any of you can't read them:
In my case, the space bar is my confirmation key, and the Z key is my cancel key. So I would use the space bar for picking my teams and characters in the character select screen.