put on kevlar boots, pants, chest, and cloth helmet. approach their group from behind, at an angle, so they don't notice you approaching. congratulations! you are now disguised amongst their group. there's so many of them that they won't realize you're someone else unless they get close enough to see your name.
now that you're extremely close and have the element of surprise, throw some grenades, blast them with shotguns, etc... with 2 or 3 people doing this you could kill off all 10 of them, because there would be way too much confusion for them to accurately decipher enemy vs ally.
if you don't have those kinds of supplies, stay off the beaten path. they're a very large group, so they're easy to notice when they come rampaging by.
besides, groups like this make the game fun, since they give the rest of the server a goal: work together to get rid of these assholes stomping all over the server like they own it.
Completely wrong, the group would have to be complete morons - we're in VOIP and immediately know everyones positions, we're always calling and know our exact numbers/placements during raids - if anyone is out of place they're dead in a second - we have a group of 11 and honestly we've never lost a single raid