Normally, this isn’t a problem. By tradition, a wedding is a formal event where guests are expected to show up either in tuxedos and gowns if part of the wedding party, or in suits and formal dresses if an invited guest.
By and large, everyone understands and accepts this. The details of proper attire for the guests is left entirely to the guests themselves. The bride has enough trouble worrying about her own and her bridesmaids’ gowns. Usually this works splendidly. Most people already know what they should wear to a wedding, or if not, they at least have enough sense to ask a mother or sister who will be delighted to explain exactly what they should and
should not wear.
Of course, even this does not always work. Now and then you find a poor schmuck with a sister who has a vindictive streak and you get a wedding guest who arrives wearing a plaid jacket, red and green striped tie and a yellow beanie with a propeller on top. But this is rare. Mostly your guests are well behaved and arrive appropriately dressed, sober and with the suitable amount of discomfort required of all wedding guests everywhere.