In this question ("When shouldn't I use 「〜さん」when referring to a third person?"), the consensus seems to be that one should avoid referring to one's own boss, coworker, etc. in an elevating manner by using ～さん.
Nevertheless, referring to other people's relatives in general still calls for a respectful manner of address with ～さん. It intrigues me what happens when these two "guidelines" overlap; for example, when your boss happens to be the husband of the person you are talking to, or when you are talking to your coworker's wife about him.
My gut feeling says using ～さん and being respectful has precedence in those cases; would that be correct?