Trying too hard

For years me and my wife were trying to start our family and not having any success. Then while attending her cousin's wedding we had a little too much to drink, ended up in bed with her older sister and had threesome. No precautions taken by anyone, resulting in my wife getting pregnant along with her sister. We now believe because we were so driven to start a family, the pressure we put on ourselves was the reason she didn't pregnant before. Totally relaxed during the threesome got both pregnant. I've now 2 children and 2 wives, but only married to one. My sister-in-law is career driven and uses her sister to raise our child. But she still joins us for sex regularly but takes precautions herself. My wife doesn't take any herself as more children wanted.