Women "tricking" men into children

My sister in law and her boyfriend have 2 children. She got pregnant with her 2nd on purpose when he did not want another child. She now is planning on doing it again because she wants a 3rd and he doesn't. Her youngest is severely autistic. Her boyfriend doesn't really want to be involved with her or the kids now let alone another baby. He supports them and pays all the bills but that's all.