Tuna's prepared for family members (5)
I believe the answer is:
aunts
'for family members' is the definition.
(I've seen this in another clue)
'tuna's prepared' is the wordplay.
'prepared' indicates anagramming the letters.
'tunas' with letters rearranged gives 'AUNTS'.
(Other definitions for aunts that I've seen before include "Relatives get a peculiar US tan" , "Relatives get bad US tan" , "Sally and others" , "Elderly female relations" , "Female relatives, usually older" .)