Question

What is the difference between they are watching their faces in their mirror and it's watching its face in its mirror?

Answer 1

Answer:

the diff is they are used for humans

and it has been used for an obj.

Explanation:

see here they are used for living ones so there you have used 'they'

and in 2nd sentence you have used 'it' we know that 'it' is used for an obj.