Generally speaking a formal intervention is always done by a professional. So it would be the spouse, it would be the parent that would retain the interventionist and they would pay a fee.

The interventionist could arrive a few days earlier and have these mock plays to go through.

They would sort of orchestrate the entire thing from A to Z. From how the sequence of events happens and who says what first and who says what second.

So it's never done by, or it's rarely done by the actual loved one, it's done by an outside professional, but initiated by a spouse or a parent.