The best wedding I went to had a total of 8 people (9 including the registrar).
The couple booked themselves in for the day, and invited 2 sets of friends which included Mrs M & me, plus another couple & their 2 kids. They didn;t tell us about the wedding, just to come for a lunch at a nice pub.
At 2pm they asked us to come for a short walk with them which turned out to be to the registry office; then we went off to a good resto for the evening.
Very romantic, great fun, no fuss, quite cheap.
Moses