.. to take some of the angst out of invitations? I propose:
Marriage Party = adult only celebration of a couple's marriage. [only exceptions being dc of immediate family]
Wedding = celebration of two families coming together to form new family.
For the B&G there would be a clear definition of their wishes and no need to explain further. Guests would then know what the rules are and can decide whether to attend and in the case of a wedding whether or not to take their docs.