They don't deny being the proprietors (6)
I believe the answer is:
owners
'the proprietors' is the definition.
('owner' can be a synonym of 'proprietor')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for owners that I've seen before include "Proprietors" , "Worsen for possessors" , "Those in lawful possession, as of house" , "Holders, possessors" , "Legal possessors" .)