The Singer sisters are lifting their voices for a cause that's close to their hearts. At age 4, Mollie (left) was diagnosed with Type 1 diabetes. Since then, she and her twin, Jackie, now both 18, have written and crooned country tunes to raise money to fight the disease. So far, they have donated more than $500,000 for diabetes research. They have taken part in fund-raising walks and charity concerts. Mollie calls Jackie her "angel." "We're a team," Jackie told TFK.