This is the place to post questions and discussions on usage and style. The members of the Wordwizard Clubhouse will also often be able to help you to formulate that difficult letter.
a. We are all smart, each in his or her own way.
b. We are all smart, each in our own way.
c. We are all smart, each in their own way.
Which are grammatically correct?
Which are natural?
Only b) sounds natural to me, though it would not surprise me if I heard c).
a) is grammatically correct, but it makes the speaker sound long-winded and pedantic.