This is terribly difficult bringing in one of the family (6)
I believe the answer is:
sister
'the family' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'this is terribly difficult bringing in one' is the wordplay.
'this is' becomes 'is'.
'terribly difficult' becomes 'st' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'bringing in' is an insertion indicator.
'one' becomes 'er' (I've seen this in other clues).
'is' put inside 'st' is 'sist'.
'sist'+'er'='SISTER'
'of' is the link.
Can you help me to learn more?
(Other definitions for sister that I've seen before include "twin?" , "Resist about the sibling" , "trade union member?" , "A kinswoman" , "Nurse, nun or relation" .)