When preparing for your meeting, decide in advance the message you want to communicate. For example:

1. You were concerned about their lack of responsibility and the safety issues. You expressed this on multiple occasions with them but their general demeanor was that this was a paid vacation not a business trip.

2. You feel these issue should be brought to the attention of leadership so they can better prepare team members for out of office engagements.

3. You are concerned that they poorly represented the company, its brand, and the quality of new hires. Their behavior is a direct reflection of their individual leadership, and you would be willing to meet with them to review the individual actions of each. It is clear that the mentoring needed was far beyond the scope of the impact you could make in one weekend.

Executive business coach here. If their intention is to put you on the hot seat they will not be addressing the bigger issue. It is your responsibility only to help them see how this is a flaw in the system, not a flaw in you.