Not part of Signal's security model, but trusting people in that chat very much can and should be part of the user's security model. If you don't trust them, why are they in the chat in the first place?
It's not a person in the chat, it's an account. The account is usually controlled by the person associated with it, but you can't assume that it's always controlled by that person.
Well the ex-wife in question can be trusted to receive it a-okay and screenshot them to send to her lawyer and cops too, depending on contents. So do US government officials. Now we just know how exactly they do it.
