I am surprised you don't know who Jenna is, as I used the default names you put in the game! Susan for Mother, Liza, the oldest Sister, Jenna the middle Sister and Rachael the youngest. I was with Liza and Jenna, and as we were all marrying each other, I should have seen Jenna and Liza kissing at the wedding ceremony (they had already had sex with each other), I should also have seen a three-way scene with me Liza and Jenna, but what I got was a scene with Jenna, and then a separate scene with Liza, who actually comes to the beach after I made love to Jenna saying she was "lonely at the apartment"!! I felt that was sad, I didn't feel I had a double marriage, but two individual marriages, making love to each wife totally separately, when I felt we should all been together. To say the ending was a disappoint is an understatement.
Also, if the youngest, Rachael is dateable, i'd love to know how, because I feel you have no chance with her in the game.