Great advice. And anyone in authority at a place of employment that might be targeted should know exactly how they intend to respond, meaning they must plan for it. As soon as the thugs make themselves known, execute the plan - get one person on 911 doing what you said, while another confronts them directly to try to force them to leave.
I wonder if there are any resources giving concrete advice on what to do in these scenarios? Kind of like how we have great standard advice from various law professionals, etc., about what to do and not do when detained by police.
Edit to add: even if you expect the local PD to come down against your side, it's probably still a good idea to call them in. The resulting time and chaos as they get things sorted out may be just enough to do something useful for the vulnerable person needing help. Remember, once that person is in the custody of the gestapo, it's fucking over, their life is wrecked at best. See only what happened to Kilmar Abrego Garcia for proof.