People who engage in that often are following a set of unspoken rules that only insiders know. They’re reinforcing their insider status, your outsider status, and signaling to the rest of the group the punishment that awaits those who marry an undesirable that is unapproved by the in-laws.
They also feel that by not actually “saying anything” they’ve retained their bona fides as “nice people” and they feel super proud of themselves as they polish their halos and hope for the day you/your husband confront them and they act like you’re a hysterical crazy person.
It may be funnier to act like you think they’re all kind of… unreliable narrators. “Has Dear Aunt Dottie gotten a baseline neuropsychological eval recently? Is anyone else noticing any family history? People keep mentioning events/invitations months after the fact and it’s concerning! I can’t think of any reason besides early onset dementia, she’s such a kind person! How awful, right before the baby! I’m not sure Cousin should be leaving baby alone with her!”