I met with Paul and Kirsty individually and explained that mediation is voluntary and it was up to them, whether they took part. It's confidential, so I reassured them that nothing would be passed on without their permission. Because mediation is informal, and outside the company's internal procedures, Paul and Kirsty were able to speak freely and tell me how they felt about the situation.
Having agreed the issues to be resolved, and the points they were happy for me to share, Paul and Kirsty agreed to go forward with mediation and meet together with me.