I caught my Brother fucking our Mother

I'm Victoria 22 answer to Vicky, I live with brother Darren 20 and mother Pamela 39 divorced. Pamela is well off financially as our father Paul pays alimony and Pamela also got a house. Paul married his PA Harriet who was the reason for the divorce and they have a daughter Elizabeth 1 together. I'm attending university and Darren works a carpenter and last March I came home earlier from the university to start on a project, Pamela wasn't in the kitchen as I expected. But I heard noises coming from her room, thinking she was cleaning something went to let her know I was home. I opened her door and saw Darren was fucking Pamela and she was horrified I had caught them fucking. Darren was off work with injured foot, he had step on a plank and big nail in the plank went thru his boot into his foot. He was to keep off it for 3 days, so he was keeping off his foot by fucking our mother. I went straight back to the kitchen followed by Pamela, then Darren. Pamela was sorry I saw what I had seen, Darren didn't careless. It was just sex between two consenting adults as far as he was concerned. I recovered quickly and I said it was only the shock of catching them at it, that shocked me being so unexpected. I had no current boyfriend, but wasn't virgin either and I'd been masturbating myself to ease my sexual tensions. So Pamela would've them as well and she was just using Darren instead. Darren was just a horny guy, I told them they should go back and finish what they had started. Pamela wasn't sure she should, Darren was willing to resume fucking Pamela. He the said why don't you join us sis and make it a threesome, I was about to tell him no way. But I started to feel a tingle between legs and decided why the fuck not and so I said okay let's fuck. Pamela wasn't sure but still joined us on her bed. Darren of course wanted to make it more than a one off, he started asking me to let him fuck me again and again. I let him a couple of times with or without Pamela joining in. First sign of a problem came last week with Pamela testing pregnant to Darren after missing two periods and I've also missed a period last month and will wait until I miss the next before getting tested. I haven't dated or fucked anybody except Darren either so Darren might have got us both pregnant.