put them in nice warm frontal light, make sure you pose them properly, that's the key to groups, you have to "build" the group so that there's not large holes and missmatched bodies.
make sure people stand with slight angles toward you, like a slight twist, with one shoulder toward you. Stack them together so that there are few large holes. Make them fee comfortable, and then watch the reading glasses, if anyone is wearing glasses you need to have them taken off, or have them tilt their head to fend off glare. You can also put short people in front but whatever you do, close up the gaps, keep them close, or you will need to spread them out and put the parents together and other family groups together.
Use a lens that will get you as close to 50mm as you can, you can go a bit below that or as high as you want and still get them in the shot, but if you go much below 40 you will introduce too much distortion. It's okay to do if you know how to control it with poses, but since youre new to this I'd stick to 40+.
Shoot it at f8 if you can. You can use a fill flash if you like but it may be useless and not necessary. I'd keep them in full frontal or slightly off to one side light, no shade on a shot like that, unless it's a big spot.
good luck and have fun, and take lost of shots. . .