I don't know if this counts as what you're looking for, but our little network of people definitely consists of more than 3 or 4 people. We aren't all involved sexually, but for the most part have at least met each other and get along. Some of us are good friends, some not so much, but we're all friendly with each other.
Our configuration is:
Me and my husband (C), who have been married almost 20 years, with two teenagers.
My husband's girlfriend (T) and her husband (G), who have been married about 19 years, with 3 kids.
G's girlfriend (J) and her husband (Z). only married a short time, no kids yet
My partner (CC), who is single and has few other partners, whom I haven't met, or have only briefly met.
I also have a partner who is deployed with the Army right now, but when we were dating, I got along well with his wife (they've been married about 12 years I think and have 2 little kids)
I've also went on a few dates with another guy (still seeing if that one works out) and I met and liked his wife (they have two little kids too).
So even if you only count the one partner that I'm actively seeing right now, that's at least 7 people in the group, most of who have met and get along well.