Arrangement with sisters

I met my now wife when I was 27 and she was 24 and we hit it off and married year later, Now I'm 34 and my wife is almost 31 and we've 3 children, quite happy living in a large house along with my sister-in-law 36 and her 2 children, I'm also the father of my sister-in-law's children. My wife was pregnant, and her sister came to stay with us after she had a nasty breakup with her partner. Depressed and feeling unwanted, my wife wanted to cheer her sister up and asked me if I would fuck her. I was somewhat shocked, but with my wife pressing I agreed and so her sister joined us in our bed. I thought it would be one night at the most two. That was almost 6 years ago now and the three of us still sleep together and I've regular sex with both, either together or just one at a time. It wasn't supposed to be a long-term relationship, but an accident happened, and I got my sister-in-law pregnant. I was slightly alarmed by it, but my wife decided as her sister wanted to have my baby. It was okay by her, and she talked with her sister, and they decided they would both share me, and I was told I now had two wives. It was strange at first, but I'm used to it now and my career is doing great, and my sister-in-law (second wife) also has a good career going. My wife prefers being a homemaker and mother to all the children. As to how many children we will have, is up to my wives as they control their bodies, not me. I just get regular use of them; I'm not allowed to take precautions myself. They take precautions if they wish too. Otherwise, it's all up to nature.