Tweed jacket of some sort, not the PC as it's day time, not evening.

Do you need to differentiate, as they are going to the event to help you and your betrothed celebrate, they doubtless know you. I don't think there is a need to have everyone the same either, in traditional weddings each man would probably wear his own tartan, that is if he was going kilted, and that isn't even a certainty either!