I have shot girl's softball team group shots in the past (12 girls plus a couple coaches) and I find a normal focal length is perfect. With your 80mm you are not going to be so close as to intimidate anyone but you will be intimate enough so hopefully you won't have to yell to be heard.

Shooting groups of people is a challenge. Just getting them to settle down and pose is hard enough, then you have to worry about someone sneezing or their eyes being closed. Make sure you take as many shots as they will allow you.

The advice about having an assistant is spot on!