Favor for my sister

I'm the youngest of 5 and my sister is the oldest and at the age 38 she wanted her younger brother than 27 to provide sperm to get her wife than 33 pregnant. Yes, my sister is a lesbian has married her longtime partner. First choice was a sperm bank, but the forms soon changed their minds. The old folktale of a turkey baster came to the fore next and it soon was dropped also. Finally direct injection by me was desired as the least troublesome method. My sister is on the chubby side and her wife isn't much slimmer, but I had agreed to donate my seed and so I fucked my sister-in-law several times. It was a get on deliver the sperm and get off style of love making. I was able to do the deed and got my sister-in-law pregnant. My sister wasn't interested in getting pregnant herself and that was it. Or so I thought, but I was asked again 2 years later to redo the whole process again and give their daughter a brother or a sister. Again, I succeed a little too well and they will have twins a boy and another girl. I was already engaged at the time and married last month the twins are due in February. My wife knows nothing of my fucking my sister-in-law, but knows I donated the sperm both times.