The concept of 'ownership' is a social construct. It depends on the morals of the society in which it operates. The BB House is more akin to a collective where goods are commonly owned and shared according to need. Most of the HMs accept this structure. However, Marcus who sees himself as a feudal Lord chooses to see ownership as a tool of power. That the internal 'laws' of the house reject his perspective is clear.
Don't measure BB House by the dominant ideology of capitalist Britain, because it is actually a subculture which dances to very different tune.