In the end of the letter, the sentence “both of you” means: 

Read the text and answer the question.

Dear Toti, 

I’m writing to you from my hotel room. Everyone else is sleeping, but I’m sitting here and watching the ocean. We’re staying at the Plaza in Atlantic Beach, and the view is beautiful. The tour is goes well. The audience is crazy about the new songs, but the fans are always asking for you. How is the baby? She has a great voice. Are you teaching her to sing yet? Maybe both of you will come along for the next tour!

Sylvia

From the book Grammar Express