I think you should rely on the expertise of the psychiatrist to identify his problem & get him to recognize what type of help/treatment he needs; there's not much else you can do; most 'shrinks' will take information from you, they just won't give you any; assuming of course they are even willing to acknowledge that he is a patient;
I'm not sure I'd be trying to do it anonymously; unless you identify yourself, your relationship and why you are contacting the psychiatrist, it is doubtful that you'll even get past the "Hello" stage.
Given your stated objective, this really isn't a financial or social security issue; you are trying to intervene to assist this individual with his problem;
I'm going to suggest that this question be moved to the medical
community in order that you might receive some professional guidance as to what, or how, or if you should even attempt to do what you want to do; there are potential laibility issues here; you'll need to disclose his age & what state
you are in as both of these may impact what you can or can not do as well as identify the risks involved; evidently the parents are still very much involved & it sounds like they haven't been exactly welcoming to your suggestions so far.....................
Hope this helps you help your friend...............................