My shy brother-in-law

I'm Catherine 34 and have 4 children, my husband 36 Eric is a know all and thinks he's perfect. He plays up on me with other women and it started not all after we married, he can play up I can't. Also, he feels trapped as his father John won't allow him to divorce me. I get on very well with John and Alison his wife. Eric doesn't work because the family is very rich, that's why Eric is too scared to divorce me. He would be cut off from the money, Eric has a brother David 31 quiet shy and very studious and completed university unlike Eric. It took me 2 years to get him to relax around me after my marriage. But we became firm friends, David doesn't drink, smoke or do drugs. Eric does all three and I think that caused him to become impotent, three years of trying no success. Anyway, I decided I should do something about it and had his sperm tested and it was proven to be worse than I thought. I couldn't tell him I had his sperm tested without his approval, so I needed another plan. Then after Eric stormed off in one of his moods, I was sitting and wondering if I just divorce the idiot. David arrived bringing some potted plants from Alison for me. I thought to myself I wished I had married David instead and decided to seduce him on the spot. I managed to do it and had 2 fucks with him. I started regularly sleeping with David and got pregnant and had twins first up. Eric didn't realize he wasn't the father, as his brain is usually clouded by alcohol or drugs. He rarely knows what he had for dinner the night before, so me getting pregnant and us not having sex didn't register in his thinking. John and Alison were delighted, David was also very happy. David and I kept up our sexual relationship and have had 2 more children together. But it didn't go unnoticed, Alison realized David and I were very close and actually caught us in bed together. But she has kept it to herself, one reason she now has grandchildren, also she knows how useless Eric is. Eric has also started having serious health problems from his drinking, drugs and smoking to excess.