My Sister got pregnant

My sister Jennifer 24 was always going out partying, I John 23 on the other rarely went out and was still a virgin. We both live our mother Janice 49 divorced, then Jennifer got pregnant and didn't know by who. Janice was really upset at the news and the fact she didn't know the father made it worse. After shock of everything had calmed down, I kept out of both of them. Then 2 weeks ago I was called by Janice and she asked me straight out had I had sex yet. No I answered and she seem a bit annoyed by my answer, but I didn't enquire why. Later on when we were all having dinner watching the T V, Janice said it's time I had sex and Jennifer you should teach him how to fuck a woman. What Jennifer said, your pregnant and you can't get more pregnant and giving your brother a fuck won't hurt you Janice added. I was shocked and stunned at the same time, then I was shocked again and Jennifer said I might as well nobody will want to fuck me while I'm pregnant incase I name them as the father of my baby. After dinner Janice lead the two of us to her bed as it was the biggest and Jennifer and I had sex for the first time. We've been sleeping together the 3 of us every night since. Janice always watches us fuck, but hasn't joined in yet.