a view point:
I discussed with the IRCTC helpline as I also came across a similar case where me and my wife had to travel but only one of the two tatkal tickets was confirmed.
"""They said that partially waitlisted tickets are not cancelled automatically and so the names of both the passengers appear in the final chart. Its only that the TT has to be informed of the same and if no other tatkal ticket gets cancelled both the people may have to share the same seat""".
But...
more... the crux is that the Ticket does not get cancelled automatically and hence if you have informed the TT and ready to share the seat,
it is Legally fine to travel with a partially waitlisted ticket."