It has fully optional sharing and only if you choose to share them. You don't even see the scene happen, you simply have two scenes where you need to get an NPC to do something for you and one possible option is to have a girl seduce the guy.
The first is to get a mind-controlled girls ex-fiancée to leave you alone after she broke up with him for you. You can tell her to talk to him or sleep with him to get him to leave you alone.
The second is when a rich woman's chauffeur catches you together and you need to keep him from telling her husband. The choices are to have her seduce him or bribe him with money.
In both cases after making the choice the girl leaves to do the option you picked and the scene ends. You can fully play this game without sharing either girl if you don't want to.
And they are both main girls.