yeah so, my sims family had woohoo together:/

okay so, on my fathers windows computer i were playing the sims 4... everything went fine my teenage kids were good in school all top grades, then they aged up and Sophus my oldest son and Anna my oldest daughter started to have this weird connection.. they were sleeping in the same bed, and i thought it would be fun to let them flirt a little. i thought that was an implemented feature in the sims 4, but NO it wasn't my friends told me that they couldn't but they thought it would be funny. it ended up that my whole family had slept together, did i mess something up in my game since my sims FAMILY- father and daughter son and father daughter and son mom and son mom and daughter father and mother?! now, i am sitting here with a mac computer (my own, i used my fathers pc before sims 4 came out for mac) that dont have that feature that i kinda want it back, just for the sake of fun! also it were halarious when they broke up and got a weird relationship ) i loved that <3

If their relationship is high enough, they will sleep in the same bed.
Same goes for grandparents and grandchildren etc.

If you checked the relationship bar, did it say that they were related? If not, then I suppose they can woohoo all they want lol
Otherwise that's one strange glitch