Complex sentence: Janelle was the class clown, and Jessica was the one with all A's they have been dancing since they were very little, they were in the school choir and they were also back up dancers at a young age.
Split into simpler sentences: Janelle was the class clown, and Jessica was the one with all A's. They have been dancing since they were very little, they were in the school choir, and they were also back up dancers at a young age.