Troubled mates in temporary accommodation will ... (9)
I believe the answer is:
testament
'will' is the definition.
('testament' can be a synonym of 'will')
'troubled mates in temporary accommodation' is the wordplay.
'troubled' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'temporary accommodation' becomes 'tent' (I've seen this before).
'mates' is an anagram of 'estam'.
'estam' going inside 'tent' is 'TESTAMENT'.
(Other definitions for testament that I've seen before include "Will - part of bible" , "evidence" , "with 1a [NEW] where is Mark?" , "books, with 1a [OLD]" , "it could be old or new" .)