Valets turn grey at Versailles occupant's extended household (6,1,5)
I believe the answer is:
menage a trois
'extended household' is the definition.
('household of three' in French)
'valets turn grey at versailles occupant's' is the wordplay.
'valets' becomes 'men' (man can mean a servant or valet).
'turn grey' becomes 'age' (turning grey is a sign of aging).
'versailles occupant's' becomes 'rois' ('king' in French - Versailles was a royal palace).
'men'+'age'+'at'+'rois'='MENAGE A TROIS'
(Other definitions for menage a trois that I've seen before include "living arrangements" , "Triangular relationship(s)" , "Unusual living arrangement" , "triangular arrangement" , "Complicated household relationship (two + one)" .)