Found in street: family that's poor … (5)
I believe the answer is:
skint
'poor' is the definition.
(similar in meaning)
'found in street family' is the wordplay.
'found in' means one lot of letters goes inside another.
'street' becomes 'st' (abbreviation).
'family' becomes 'kin' (synonyms).
'st' enclosing 'kin' is 'SKINT'.
'that's' is the link.
(Other definitions for skint that I've seen before include "Strapped for cash" , "Stony-broke" , "Broke (slang)" , "bust" , "On one's uppers" .)