My forgetful Sister

My sister Leslie 25 is so forgetful that she has write things down so not to forget. Usual day things she doesn't forget, but birthdays and other similar events in the future slip her memory. So she has to be remind regularly by anyone concern, I'm her nerdy brother Kevin and only sibling and the oldest of us at 29 I got a good career after university and doing very well for myself still living at home with my mother Karen 46 widow and I've been fucking her since my father passed away 3 years ago in a car accident with his parents. Leslies lives with and is usually out with friends, so we have plenty of spare time to fuck. Leslie needed a car to get around as our town doesn't have any taxi service or public transport and bicycles are not the best transport for the hilly town area. I bought a new car after our father's car old broke down too many times. She was using it to get to work and where ever she was going. Anyway my birthday came and Leslie had forgotten as was fairly usual for her and with Karen away to visit her sick mother we were alone that rainy weekend. Karen rang me first thing in the morning waking me and told she give a special gift on her return. This got me horny, I had breakfast and asked Leslie what she was doing that Saturday and she nothing planned as it was raining and had been for 3 days. With no work she was staying home, shortly after our grandparents rang and Leslie answered the phone and they asked to speak to the birthday boy. She passed me the phone to me and went to her room. Shortly after I had finished on the phone, Leslie said sorry for forgetting my birthday. No worries I said and she said had wanted to give me something special. Because I'd gotten her the car, I said don't worry about it and as I was looking at her in skimpy top and short shorts I got aroused and a hard-on. It made a bungle in my pants and Leslie noticed like she usually did, as I had gotten them regularly around her over the years and I think she dressed to cause them as a joke. But this tine instead of her usual smirks and quips, she removed her top completely showing me her breasts no bra. I was at a lost and she then pulled down my pants to expose my hard-on and said nice cock. She started to stroke it and I kissed her and took her to my bed and without asking removed her shorts and panties. She didn't try to stop me and we fucked and after while laying beside I got aroused again and we fucked again. We ended up fucking all weekend and every night until Karen got home. But I wanted Leslie now all the time and got hard-ons almost every time I saw her. Karen knew I had fuck Leslie, mainly because we had fucked in her bed and left cum strains on her sheets and also we had already said we had stay home together. She wasn't upset by us fucking, but it was her who asked Leslie had she updated her protection as it was almost expired before Karen had left. Karen had to remind her all the time, Karen knew straight away Leslie had forgotten by the look on her face. So two things happened, Karen got a test kits and told me I should try for a transfer closer to our grandparents. The transfer wasn't hard to get as the company had offices there also and me saying I needed to be closer to my aging grandparents also helped. Once the first was used a positive result showed and another and than another all showing positive results. No worries there are tests and if the baby is healthy that's fine also. The test were had and showed no problems and I now have a beautiful baby daughter. Leslie and Karen now join me every night in bed, only our grandparent know I'm the father of their great grand daughter and they won't say anything to anyone outside the our family group. Karen stopped precautions because she thinks she passed having babies. Pity