'Open marriage' by another name. The situations I am familiar with wound up with really messed up kids. Totally disfunctional situation.
Not exactly. I had friends who tried an open marriage against my advice, and it ruined them. But that was sex outside the marriage with different people, basically a license to cheat.
In this case we're talking polyamory, basically one big marriage, everybody loving the other as husband and wife, and in this case wife and wife. Notice this one didn't dissolve until someone cheated -- went outside the marriage -- just like in a real marriage.
Still, are they out of their minds? Especially when children are involved!