Another like Eva and Juan possessing son like theirs (5,6)
I believe the answer is:
third person
'like theirs' is the definition.
('theirs' is a third-person pronoun)
'another like eva and juan possessing son' is the wordplay.
I cannot really understand how this works, but
'another' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'son' could be 's' and 's' is found in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for third person that I've seen before include "He's the one" , "stopped by Ancient Mariner?" , "She perhaps" , "will suggest PC title for Greene novel?" , "reason for an eternal triangle" .)