Well, the consultant can't without breaking medical confidentiality, except in some very specific circumstances involving potential harm to others and/or if legally compelled. As I think @mauvishagain has said.
And I don't see why the others would want to invite scrutiny, even if the circumstances are roughly as described (which seems unlikely).
Is 'Polly', if she exists, at all likely to want to weigh in and support a former friend she presumably supposed she was doing a favour for, but who depicted her in her bestseller as Queen of the Meat Packing Shed (which has no residential planning permission), an insensitive exploiter of a seriously ill man and a duplicitous landlord, telling the Walkers to stay forever but showing paying tenants around when they're out?
Or even Anna, if she exists, whose Polruan flat is depicted as glum, small, dark and with a view of rats and a cliff face? It doesn't exactly sound inviting to potential tenants, if it's still being let...
And OK, Dave and Julie are pretty much the only two characters in the books outside of TW who escape any glumwashing from SW, but even then, would you really want to invite public scrutiny, or put yourself out there in the media as a supporter of someone who's been fingered as an embezzler at the very least, and as a writer of a significantly dishonest memoir?