sin or deres? · sin egen

The rule is the same when the owner is plural. Use sin, si, sitt, sine when the subject owns the thing: Naboene selger huset sitt (The neighbours are selling their house). Use deres (their) when the possessive is part of the subject or the owner is someone other than the subject: Huset deres er til salgs. Vi passer katten deres.

egen (own) stresses who the owner is. It agrees with the noun in gender and number, and unlike other adjectives it keeps that form after a possessive (min nye bil, but min egen bil):

• egen with masculine and feminine nouns: sin egen bil
• eget with neuter nouns: sitt eget rom
• egne with plural nouns: sine egne barn

With egen the possessive stands before it and the noun stays indefinite: De har sitt eget hus.