Gorgeous fat chick, her husband obviously can't handle her anymore. And he's not really interested in her either! Such a body shouldn't stand idle for nothing! He should also thank his son - the lady gets everything she needs at home and will definitely not be looking for a lover on the side. All in all, everything is like in a normal Swedish family, everyone is happy! In my opinion it is better for him to share his wife with his son than for her to go out with some strange man.
To tell you the truth, considering the age of the brother and sister, it is quite normal that the brother became aroused by the sight of the naked girl in front of him. Maybe what happened next is not part of the plans of normality, but tell me honestly, would you resist such a dark-haired beauty? That's what I mean.