I got my Drunk Mother Pregnant

I'm Sam 25 living at home with my parents and younger twin brothers. My father Charles was 49 at the time and Mother Joanna 44 and one weekend last February my siblings went to visit our father's parents. I have a job and was required to work and on getting home my parents were arguing and Charles stormed off. Joanna as was normal for her starting drinking after the fight, only time she drink heavily. Anyway I went to my room to get out of the way. Later on my cellphone rang and it was Charles he was staying the night at his brother John's place and I was to tell Joanna. So I went to tell her and she was already pretty smashed as they say. I don't think she heard much at all, except for saying Charles name as saying dad or daddy didn't register with her. She start talking to me like I was him, saying she was very horny and he should the right thing by his wife and fuck her. That was the first time I'd ever heard her swear, it aroused me a bit also. Anyway I told her to go to bed and she said only with you honey meaning my father. I helped her to her bed which she sat on and started undressing, telling me to do the same. Anyway seeing her breast got me excited and I got a hard-on and with her wanting sex and me horny. Why not she passed having babies I thought and so I got into bed with and fucked her. Which made her happy and she went to sleep I laid beside her for a while thinking about actions. Got aroused again and mounted again and fucked again, I thought I better clean her up and so I did and dressed her in PJ's. I went to my bed and Joanna awoke late on the Sunday just before noon and Charles was home by then, she didn't say much and she was hungover. She never mention their sex the night before and he didn't mention he stayed at John's. By Monday morning things were normal and twins were home and mucking about as usual before school, Charles left for work I soon followed go to mine. Joanna took the twins to school as usual. The following weekend. Charles and Joanna had sex I know because I heard the bed squeaking. The twins were out so they made love. Anyway I thought nothing more of me fucking Joanna until she missed her period, they would talk quietly and Charles said he had used a condom. She said it must've broke or split. I read online about imported condoms that broke during sex, I checked Charles condoms and they weren't the same one. But when I was at the shops and saw the brand was supposed to be unreliable and bought them a packet as it was a similar color to Charles brand. I got home no one else home I went to his bedside table and took his packet and replace with the ones I had bought. Removing condoms to be make it look like they had been getting used. I threw the extra ones in the neighbor's bin and kept the brand Charles had been using. Again I heard them talking about getting tested, Charles again saying he used a condom. This time I asked what brand and at first into trouble for listening in to their personal conversation. I just said I saw a thing online about brand of imported condoms that had a high failure rate. Asked what brand by Joanna I said I can't remember, but would look it up. Charles said he never used imported condoms, but Joanna got the packet from his bedside table. I had printed out the story and the picture of the package matched the blue packet Joanna had in her hand. Joanna and Charles were stunned, Charles said he never buys imported condoms again. I asked what color is the packet you buy. Blue, but I checked the name also he said, I said I've got the wrong thing sometimes. But the packet was the wrong brand and it was proof they had use the faulty condom. Enough to stop them arguing over who's fault it was, after Joanna missed her second period. She got tested and was confirmed as pregnant and more test later show we're getting a sister. I'm in the clear.