All of those people might be good to contact. If it is serious, in my opinion, I'd start with the police. If less serious, then you may not need to contact the police.
One of the difficulties, sometimes, is that individuals getting care at a care home may have cognitive impairments and/or hallucinations. They may think something happened that did not. However, because they can't protect themselves as easily and may not be believed, they sometimes are targeted for bad things. It can make it hard to know what to do.
In addition to your list, I'd add the social worker at the care home and the ombudsman as folks you can also turn to for help.