Longevity is rare in today’s music business. But long before smartphones and Spotify streams completely transformed the industry, Hong Kong had Twins, the Cantopop duo composed of Gillian “Ah Gil” Chung and Charlene “Ah Sa” Choi. Chung, now 45, and Choi, 43, have, save for a brief scandal and hiatus in 2008, been near-constants in the public eye since their debut as Twins in 2001. Over two decades on, the two are still at the top of their game, set to perform in Hong Kong this December in a...