I'm listening to Mike Duncan's Revolutions podcast, and in the most recent episode he discusses Mary Antionette and Louis XVI's marriage, and while talking about their reluctance to consummate the marriage the night after, he says that "there was probably a roomful of people milling about, as was the weird Royal custom." Were the Dauphin and Queen-to-be to be really expected to bone down in a roomful of aristocrats, or is it something more innocent?
According to André Castelot's Marie Antoinette the court gathered in the bedroom to watch them put on their night clothes, and for the archbishop of Reims bless the bed. The drapes of the bed were closed and opened again, and then the king left, followed by the court. Antonia Fraser's book with the same title describes the same ritual, but doesn't mention the drapes. The Lost King of France by Deborah Cadbury doesn't say they weren't there, but mentions that the sheets would be inspected for blood the next morning, which means the court wouldn't have known immediately if the marriage was being consummated.
So they were left alone. It would probably be awkward enough to have your grandfather lead you to the bed on your wedding night, though, like Fraser describes.