1. Belonging to them

Sounds like: there's

Encyclopedia: Theirs

• unnaturally
• unnaturalness
• unnavigable
• unnecessarily
• unnecessary
• unneeded
• unneighborliness
• unneighborly
• unneighbourliness
• unneighbourly
• unnerve
• unnerved
• unnerving
• unnervingly
• unneurotic
• unnilquadium
• unnotched
• unnoted
• unnoticeable
• unnoticeableness
• unnoticeably
• unnoticed
• unnourished
• unnumberable
• unnumbered