Old aunt and gran upset a relative of ours (9)
I believe the answer is:
orangutan
'a relative of ours' is the definition.
(a relative of humanity)
'old aunt and gran upset' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'and' says to put letters next to each other.
'upset' indicates an anagram.
'aunt' put after 'gran' is 'granaunt'.
'granaunt' with letters rearranged gives 'rangutan'.
'o'+'rangutan'='ORANGUTAN'
(Other definitions for orangutan that I've seen before include "a big sub-human creature" , "ape" , "Primate" .)