Announcing Adoption to bio sisters mother...

Vanessa • Xavier Michael & Zachariah Heath 8.8.16 💙💙 Willow Evelyn due 6.11.17❤️
Currently the twins I am adoption are 12w1day <3. About 10 people know, close family and friends :) I am having trouble finding a way to announce because I know of one person inperticular who is going to be very negative about it. She is very judgmental and  thinks her opinions and views about any situation are needed or justifiably. She is the mother of my brothers second daughter (my niece) and has extremely ill feelings about my brother due to there relationship before my niece was born. (He is allowed no part in her life per my nieces mothers request and we all respect that as her choice) My niece is almost 6 now and her mom still won't let her see her older sister, my other brothers daughter, who is around the same age (even if I or my mother have both girls and my brother is not around). It is a very messy and emotional situation. I just fear that when she hears about me adopting the twins (my brother is the biological father) that she is going to bash everything and anything about the babies & the pregnancy. It will be a private and independent adoption, the birth mother and my brother want to sign off all right competely and just be auntie and uncle because that's what's best for the babies. So now I just don't know what to do. She uses my niece as a pawn and always has. My family and my self have always bent over backwards and catered to her to have the strong relationship with my niece that we have. Please someone give me advice as to the best way to go about this. I honestly don't know what to do.