where's the line with the husband when the wife is the contact person

genuine question i keep getting wrong. lots of couples i meet, the wife is the one who does all the messaging on the app and once we're actually meeting in person the husband suddenly wants to chat one-on-one or starts messaging me directly between meets. nothing inappropriate exactly but it makes me uncomfortable because i don't know if she knows. i'm in sydney mid thirties, been in the scene maybe four years. how do you push back to the husband without making it weird and without throwing him under the bus to her... what's the etiquette i'm missing here...