In the past couple of days, Billy Rand had uploaded various videos introducing the mod versions of incest, teen pregnancy, and marriage for the Sims 4 version. The modules that were in use in the past were much more bizarre than the ones that are introduced now. The changes in the Sims 4 version have made things more subtle otherwise, gamers were at times grossed out by modifications such as the inzest mod. However, this mod still exists in the new version, but in a different manner.
The Sims 4 polyamorous trait will allow your Sims characters to have multiple relationships.