Primate’s brother’s inviting one in (5)
I believe the answer is:
loris
'primate's' is the definition.
(I've seen this before)
'brother's inviting one in' is the wordplay.
'brother's inviting' becomes 'lors' (I can't explain this - if you can you should believe this answer much more).
'one' becomes 'i' (Roman numeral).
'in' means one lot of letters goes inside another.
'lors' going around 'i' is 'LORIS'.
Can you help me to learn more?
(Other definitions for loris that I've seen before include "Small nocturnal primate" , "Nocturnal primate of Southeast Asia (usually slender or slow)" , "Short-tailed mammal" , "Slow-moving nocturnal primate" , "lemur" .)