Complex sentence: Hatfield was the only vocal on Unchained Melody and Ebb Tide; both "Ebb Tide" and "Unchained Melody" were songs Bobby Hatfield had performed with his first group, the Variations.
Split into simpler sentences: Hatfield was the only vocal on Unchained Melody, as well as Ebb Tide. Both "Ebb Tide" and "Unchained Melody" were songs Bobby Hatfield had performed with his first group, the Variations.