A Favor for my Sister

I was 30 single and good career and was between relationships, as the youngest of 2. My sister 35 is a lesbian, decided she needed my help. Her partner 36 had gotten clucky according to my sister and want to have a baby. Her partner was an only child and really wanted to be a mother. Obviously, my sister wanted a blood relationship with the child, and she got the idea I get her partner pregnant. She would be a blood relative at least and so she asked me straight out, always straight to point my sister. Shocked of course, but interested also and agreed and told her to make whatever arrangements she needed too. A week later she called and said the legal process was taxing and asked would I do a straight injection. Which in her words would cut out the crap, I said OKAY, and the arrangements were made. A threesome arranged and I fucked her partner twice and then two weeks later repeated it again. Finally, after the fourth attempt a positive result and she was indeed pregnant and would've a son, named after me. In the 2years since another child was wanted and I again enlisted to perform the required deed again. I had just married, and my wife was pregnant and knew of my being the father of my sister's son via her partner. My sister didn't ask me directly, choosing to ask my wife first and on getting approval I was duly informed. Same procedure as before except a foursome, 6 attempts before success this time and now months later my sister's partner is having a much-wanted girl. My wife had a girl last month, due to everything involved my sister and her partner bought the house next to me and my wife. All our parents know of our actions and are happy with it and the results, including my wife's parents. I'm just the donor for my sister.