Just gonna quote some things from your application that are wrong..
gather evidence and bring them up in the lead team meeting. If it wasn't that serious i would kick them and warn them not to join back and abuse then i would again bring them up in the lead team meeting.
As you get trained you get told that you cannot use your powers against other staff members. As you mentioned above
. As you already should know cannot do this!
If they still refuse to apologise then i would suggest that they try to not play at the same time.
This is weird, if staff cannot handle each other they should resolve the problem. If they cannot go along with each other as grown-ups they shouldn't be staff. Giving them an option to not come online at the same time is not a solution to a problem. As for example TTT meetings, they would most likely be there and thus arguments would be able to continue if left unsolved.