Chapter XX (pages 624 - 643) in the Robert's Rules of Order 10th Edition covers disciplinary procedures. It's a long, complex process. And, it won't help if your by-laws don't already reference Robert's as your PTO's parliamentary authority.
Does your PTO by-laws include a Code of Ethics clause? Does it describe how ethics violations will be handled?
One of the officers in our PTO is causing some problems at school. The main issue is her telling lies about certain parents in order to gain more teacher support.
I thought I remember reading in an article about Robert's Rules that there was a way to ask for an inquiry into the actions of an officer. From that inquiry they could be removed form office.