A small company's custom is to share accommodation (7)
I believe the answer is:
cohabit
'to share accommodation' is the definition.
(I've seen this before)
'a small company's custom' is the wordplay.
'a small company' becomes 'co' (abbreviation; 'small' indicates a short form).
'custom' becomes 'habit' (habit is a kind of custom).
'co'+'habit'='COHABIT'
'is' acts as a link.
(Other definitions for cohabit that I've seen before include "What to do with partner" , "Live together as unmarried couple" , "become bedfellows" , "What some items do" , "Share residence" .)