both of theirs

Pronoun

colloquial

(colloquial) That which belongs to both of them; the possessive third-person plural pronoun used without a following noun.

Japanese Meaning

彼ら両方に属するもの、つまり二者それぞれの所有を示す表現 / （口語表現として）名詞を伴わず単独で用いられる第三人称複数所有代名詞の用法

The old journals on the shelf were both of theirs, filled with shared memories.

棚の上の古い日記は二人のもので、共有された思い出でいっぱいだった。

Sense（1）

(colloquial) That which belongs to both of them; the possessive third-person plural pronoun used without a following noun.

That lottery money is both of theirs. They ought to share it.