Family goes on vacation to northern capital (8)
I believe the answer is:
kingston
'capital' is the definition.
(capital of Jamaica)
'family goes on vacation to northern' is the wordplay.
'family' becomes 'kin' (synonyms).
'on vacation' means to remove the middle letters (after the inside letters have vacated the word).
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'goes' with its centre taken out is 'gs'.
'kin'+'gs'+'to'+'n'='KINGSTON'
(Other definitions for kingston that I've seen before include "Royal borough on river Thames" , "Jamaican capital" , "Capital of Jamaica" , "island capital" .)