Amistades

Amistades
 

I writing a sentence about something and need to translate the phrase '...and their friendship...' their being plural, so can't decide if it should be,

sus amistad
sus amistades
su amistad

though now looking at it leaning towards the first.

¡Muchas gracias por su ayuda!

"Sus amistad" makes no sense at all; the possessive and the noun must agree in number.

"Amistades" in plural refers to friends.