(reference to popular tv/culture) In Game of Thrones, the term Ward would cover this I think?
Theon Greyjoy is a Ward of House Stark, left in their care lest the Greyjoy's move against the larger house. Very much a 'hostage'.
True. Maybe a half-dozen additional races, but with a deeper culture to draw on and different factions within those races.A few humanoids that don't just become someone you kill but an interesting opponent and possible ally is more fun.