Conspiring to enact a seditious coup de etat is not a formal Constitutional duty of President and Vice President.
Both the claim of conspiracy, and the characterization of a "seditious coup d'etat" are legal conclusions, not statements of fact. Unless there is evidence that they discussed such things eo nomine, a presumption of executive privilege would most likely apply.
Furthermore, the point of things like executive privilege is, primarily, to shelter from public display precisely those sorts of discussions that don't lead to actions, but which might have involved discussions of misconduct.
It's like the First Amendment - the First Amendment doesn't exist primarily to protect "nice" speech that all and sundry can agree is acceptable; it exists primarily to protect from punishment those whose speech is considered "bad" speech by the majority.
