To establish whether anybody is 'tone deaf' would require expert medical opinion, as would establishing whether that condition has been passed on through the family or merely a single occurrence - an isolated accident of birth.
Arbitrary diagnosis by non-experts would be both highly irresponsible medically and would act as a disincentive to anybody wishing to attempt to sing.
I would be interested to learn if you have expertise enough to diagnose 'tone deafness', or whether the above has been cut-'n-pasted from the internet.
'Tone deafness' is one of the most common reasons given by people for not being able to song; in every case I have come across it is an unqualified self-diagnosis never backed up by any medical examination whatever. It is a cop-out for not putting in the effort, usually arising by having been told by non-experts that they are 'tone-deaf'.
I would also be interested to learn what experience you have of working with aspiring singers.
Jim Carroll