OK, the update
DH and BD12 went to SD23's graduation ceremony. As far as I know they had tickets, it was outside and I've only seen one picture of SD23 taken before the ceremony and from very far away.
SD23 called to talk to BD9 the morning of the graduation but it was the weirdest conversation. She asked what BD9 was doing, BD9 told her, and SD23 said, "Well, I'll let you go back to what you were doing." End of conversation. I don't think BD9 knew what to think of it. I suppose SD23 was just placating DH by talking to her, or trying to prove she has a "good" relationship with BD9.
SD moved out of our house and in with BM when SD was 15 and BD9 was 2. BD9 has seen her fewer than 10 times since then and spoken to her on the phone probably less than that.
DH didn't act overtly mad at me BUT he did deliberate drive straight through the town where my mom lives and stop for a bathroom break, then drive on, THEN call my mother's house and talk ONLY to her. Weirdo.