We've just been through a really intense moderation process and pilot with another internal moderation team with one of our clients. One thing, since it sounds like you're still fairly new, is that you can use your new-ness as an excuse to level-set with these people and bring clear, documented evidence that their actions are not in alignment with the program's values (said in a nicer way) and put some really clear boundaries down. It's going to require a fine balance between authoritative and curious.
For the larger process, I think you'll need to get clear documentation of the complaints leveraged against these people and start to put those gray areas into the guidelines for the leadership program and for the community at large. If there isn't a clear process for reporting these complaints and they've just kind of bubbled up, that also needs to be remedied.