あなたたち would be a bit rude if you say that to friends or colleagues; when a professor talk to his students, it would be acceptable.

あなたたち (you guys) can be used in rather formal situations from a person with a higher status to the lowers; for example, from a teacher to his/her multiple students, a boss to subordinates, from a sempai to kohais. The other expression in the same situations is きみたち(きみ=you, たち=guys in this case). This is more casual and works in any above situations. The further more casual expression is きみら. For example, to close subordinates. I often use this. 皆 (みんな; you guys, everyone) is plural in Japanese. We do not have a singular form for everyone in Japanese. This expression is used among friends with the same age and can be used to close older friends and sempais. The formal expression is 皆様 (みなさま) (NOT みんなさま), which can be used from companies to customers, at conferences, at companies’ meetings, etc. 皆(みな) sounds very old fashioned in conversations (like samurai movies), but could be used in written sentences.

よろしく