With a small company the custom is to share accommodation (7)
I believe the answer is:
cohabit
'to share accommodation' is the definition.
(I've seen this before)
'with a small company the custom' is the wordplay.
'with' means one lot of letters go next to another.
'a small company' becomes 'co' (abbreviation; 'small' indicates an abbreviation).
'the custom' becomes 'habit' (habit is a kind of custom).
'co' next to 'habit' is 'COHABIT'.
'is' is the link.
(Other definitions for cohabit that I've seen before include "Live together as unmarried couple" , "Share a property" , "What to do with partner" , "What some items do" , "Live together, married or not" .)