That would be a drawback whether it was polygamous or polyandrous.

The civil issue John describes seems straightforward; the responsibility for child Z is carried by his father X and his mother Y. If they are also married to other adults A,B,...n, it has no bearing on the parental duties for that child. In other words, it is an independent issue. If that burden transfers by reason of legal action, as it sometimes does in dual-person marriages, so be it.


A