The highlight should only be visible on the unit you selected. I'm not sure I understand you correctly here; you're getting green arrows even under troops you didn't select? If so, I've never come across that before, and can't seem to find any information on it. You might want to wait for an EB team member to come by. I did find something that might be related, though; this forum thread might have a solution.
Also, regarding removing the strait graphics, this site appears to have a solution, though I've never tried it myself.
Sorry I can't help you much. I hope you manage to fix this issue.
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