I agree with Harris here. Kettlebells are tricky, and correct form is mandatory to avoid wrist injuries. Even though it is the latest ‘thing’, I would think about it twice.
I personally bought one adjustable kettlebell and only use it one-on-one when I do. Since you are doing a small group of up to 5 people, it could be one station of a circuit format which would save you buying lots of them and log them around.