Agree that detachment is the right approach. if *he* wants to talk to his sister on your behalf and let her know how unacceptable it is to talk badly about you or your child, he can feel free. But it shouldn't be your responsibility. (Also, that is terrible that his sister would talk like that about a child!! I'm totally on your side on this.)
Me (46) H (42) M:14 T:18, D9 & D11 4/19 - 12/19: series of escalating BDs 9/20 - present: R and piecing
