I'm never keen on this sort of thing either; and, like Kim said, I tell them they need a professional but the reply is usually 'We can't afford that - it's you or somebody with a basic point and shoot, and no knowledge or experience'.
When forced, and in suitable locations, I treat it as a wildlife shoot and try to get a few individual portraits or small groups who are doing their own thing within the wider scene. The formal group pose is my least pleasant experience of any shoot.
And the one thing I won't do under any circumstances is weddings.
So well done for tackling the challenge, Kim.