Breaking Dawn's Renesmee will be played by 10-year-old actress Mackenzie Foy. She is Renesmee.  However, she will also be played by three other young actresses -- Eliza Faria will play Renesmee at age 5, Rachel St. Gelais will play Renesmee at age 6, and Sierra Pitkin will play the oldest Renesmee -- but not the way you might think. After all, it wouldn't be much fun to watch a character whose fa…