Impersonate Little John, brother (9)
I believe the answer is:
dominican
'brother' is the definition.
(I've seen this before)
'impersonate little john' is the wordplay.
'impersonate' becomes 'do' ('do' can mean to do an impression of).
'little' becomes 'mini'.
'john' becomes 'can' (both can informally mean toilet).
'do'+'mini'+'can'='DOMINICAN'
(Other definitions for dominican that I've seen before include "West Indian" , "Republican" , "Caribbean islander" , "Religious" , "One of many brothers" .)