15-year-old Lennon Stella and 11-year-old Maisy Stella play sisters Maddie and Daphne on one of my favorite shows "Nashville". But they're also sisters in real life, who got their start covering songs on YouTube, just like Justin Bieber.

Their first big video was a cover of "Call Your Girlfriend" by Robyn, and it's been viewed more than 25 million times since its debut 3 years ago.