Oust terrible aunts, embracing Bertie finally (6)
I believe the answer is:
unseat
'oust' is the definition.
(thesaurus)
'terrible aunts embracing bertie finally' is the wordplay.
'terrible' indicates anagramming the letters.
'embracing' is an insertion indicator.
'finally' indicates one should take the final letters.
The last letter of 'bertie' is 'e'.
'aunts' with letters rearranged gives 'unsat'.
'unsat' going around 'e' is 'UNSEAT'.
(Other definitions for unseat that I've seen before include "Remove from horse (or house?)" , "Remove from power" , "Throw (as a 15?)" , "Dislodge from saddle" , "Get out of office" .)