Loose family members one's seen in lodge (9)
I believe the answer is:
freemason
'one's seen in lodge' is the definition.
(Freemasons meet in lodges)
'loose family members' is the wordplay.
'loose' becomes 'free' (synonyms).
'family members' becomes 'ma son' (ma and son, mother and son).
'free'+'mason'='FREEMASON'
(Other definitions for freemason that I've seen before include "secret society member" , "who could be in order" , "His order's a secret one" , "lodger?" , "who's in order" .)