HELP: "My Brother’s Wife Wants Me To Impregnate Her"

My elder brother is sterile and his wife is asking me to help her get pregnant.

I am in a state of confusion as I write this. Just last month, we had a naming ceremony for my third child. I have three boys. The whole family was here for the naming. My elder brother by four years has been married for eight years no children and his wife always calls me each time my mother or siblings put pressure on her to give them a child.
I always comfort her that they would surely have a child of theirs in God’s time. A week after the naming she called me and said she wanted to talk to me in private. She came to my office during my lunch hour and together we went to a nearby eatery. She moped on and on until she dropped a bomb shell. My elder brother is sterile. I thought that was all. She now suggested I get her pregnant since “we are all family”. And that my system is “full of boys”.
She actually pleaded and even shed tears. I was so shocked. I was so touched. I asked her if my brother knew of her plans but she said no and that he has refused to accept the results of different tests they had conducted. Should I tell my elder brother?