While it may not be a 100% concious decision, it's rude and inconsiderate.
They do not kiss or have penetrative sex with others.
I would suggest talking at length with your husband and finding out what his motivations are.
Truthfully, this would make me really question the marriage.
We played a little while the other couple finished up, and then we all went to the hot tubs.
My husband brought this up to me not to long ago.