Possessive adjectives don't take the -s of the plural with plural nouns (our students, not ours students).
his = of a man
- His name is Paul.
- My husband is old. His hair is grey.
her = of a woman
- Her dress is beautiful.
- Her name is Maria Callas.
its = of a thing
- Its name is British Bank.
- The car is new. Its colour is red.
their = for groups of people, for things
- Their names are Stephen and Larry.
- Their rooms are dirty.