I have a young married friend who told me that he finds it awkward when his wife’s brother comes for a Shabbos meal with his wife.
I’m glad someone brought up family relationships in this conversation. The Gemorah (Pesachim 113a, similar Bava Basra 98b) says that one must be careful with his wife and his sons in law. I find it difficult that we are discussing not having couples together, but we ignore the Gemorah and have sons in law by their Shviggers!!! Especially when the gemorah says about it that people must be careful.
One who is “sensitive” in these areas (eating with the opposite gender) must be sure not to go to their shvigger for meals, and certainly never to sleep at their home, CV! Also one must not invite their son in law for a meal or have them at their house.