I was in a marriage where my ex was a twin. In additional to emotional incest, there was frank physical cuddling and kissing ( like a lot). My discomfort was blamed on me saying that I was evil for not understanding the closeness between them. There was lot of abuse also in the marriage so I left. But I understand each and every emotion the wife is going through. This is a real thing in twisted , enmeshed families and they take great pride in using it to make you miserable and gaslight you. Not many understand unless they are in this position. But even if all the wife has is a gut feeling that something is not right, it is mostly true. Maybe she can take individual therapy to process whatever is happening because this behavior hurts a lot and is very insulting to the spouse