Making Babies

I'm Alexander 24 answer to Alex, I live with my mother Georgia 43 and sister Robyn 26. My father fucked off years ago and we haven't heard from him since. Both my mother and sister work at the local hospital as nurses and work shifts. I'm a carpenter and am usually home most nights. I'm not the greatest when it comes to dating, but have had some success. We live on a corner and have a warehouse behind our home and so only have one house beside ours. The house is owned by James 40 and Martha 38 and they have been there for about twelve years. They have been trying to start a family for almost as long and hadn't had any luck. Martha is great friends with both Georgia and Robyn and she has always claimed I'm the splitting image of James when he was my age. I didn't take too much notice of that, but then in October last year. Martha came over when James was away for work and both Georgia and Robyn were at work. She had got tested and she was okay and secretly had James's sperm tested and it wasn't great if they wanted children without help and even then it wasn't good odds. Martha told she was sitting in their garden and thinking how she could break the news to James about his sperm problem. On seeing me, she got this idea I could provide sperm and get her pregnant and James wouldn't need to know. Especially if I agreed to provide the sperm on the quiet, so she did some enquiring into what she needed to do and when to do it. So then she came to ask me to provide the sperm, at first she went around the subject. Finally she asked me to provide the sperm I was shocked at first. But I finally agreed to her request and asked how were we to proceed. Martha is not slim or overweight and more towards being called plain than being called beautiful. But totally fuckable in my book, but similar to both Georgia and Robyn in size and weight. So I asked how she wanted to proceed and I masturbated into a jar and Martha done what she had too with it. After several weeks no positive results and when James had to go away for work again. She wanted to try again, with both Georgia and Robyn at work Martha asked me over to their place. This time she wanted me to fuck her and deliver my sperm straight towards her egg she said. It was awkward at first, but I done as she requested. After our fuck we were laying beside each other and then she started to play with my cock and asked was I willing to make another delivery. Why not I thought and we fucked again, 3 more sessions followed before James got back home. After awhile I started thinking it had failed again, but then James and Martha came over and told Georgia and Robyn they were going to be parents. I wasn't home and I was told on getting home, I was happy at the news. It was several more days before I saw Martha alone and was told that we had succeeded and not only that, Martha also told me she was having twins.