My Sister in Law Wendy

Long story short, I Allan 43 married to Lisa 41 and have 3 children. Lisa has a younger sister Wendy 37 single little overweight and very conscious about everything. Anyway last March at her birthday party Wendy was saying she wouldn't ever have children of her own as she couldn't find the right man. Lisa was trying to cheer her up and not doing too good, Wendy started drinking more and more. By the time everyone had gone home, Wendy was smashed. Wendy was staying at our place and was in town for the party and a visit. Lisa helped me put Wendy to bed and as we walked to our room, Lisa said I wish I could help Wendy find a man or even just have a baby. I stayed quiet, as we got ready for bed Lisa asked me about donating sperm for her to get pregnant, I still stayed quiet. Hoping it would pass. But as we laid together I made the usual move with Lisa to have sex with her. Lisa said no, we have to help Wendy. I asked what can we do, its not like I can go in and fuck her now and hope she gets pregnant. Lisa eyes opened wider and replied why not, I taken by surprise. Then answered for one thing if she wakes up and screams I go to jail. Not if I'm with you Lisa replied, how does that change things I asked. I can say we were having a threesome and she won't complain. Lisa then asked me straight to fuck her sister and I know my wife once she sets her mind to something, your wasting your time trying to change her. So I said you will have to have sex with me also for your story to ring true. I wasn't thinking clearly and that was the best I could come with at the time. Lisa then said we'll need her in our bed to make it look right. So I followed Lisa to to Wendy's room and we both helped her to our room. Lisa undressed her and then helped me get her ready for sex. I fuck Wendy and left my sperm inside her and then anted sex with Lisa who let me as long as I left my sperm in Wendy again. Which I did then we all slept together in the same bed. In the morning I was up first and had quick shower and after went to check on the children. I started making them breakfast and they were eating it when both Lisa and Wendy made an appearance. I knew by the smile on Lisa's face that Wendy was okay with having a threesome with us. Wendy seemed happier than she was before, but I didn't think much of it at the time. Only later was I told by Lisa that Wendy would be sharing our bed until she returned home. What was my response, but Lisa added what's wrong with fucking Wendy a few more times before she go home. I didn't have reply so stayed silence. A week later Wendy returned home and in May she called Lisa telling her she was pregnant/ Lisa was happy for her sister and I asked how she going tell the rest of the family that's pregnant and I'm the father. That took the smile off her face fairly quickly, but she thought for awhile and said we'll tell the truth. How that I asked, she added we were all rather tipsy after the party and had a threesome. That's the easy way, tell the truth she said, I just said you tell them and leave me out of it. She smiled and in June I was told Wendy had gotten a transfer and would be living us and having her daughter.