PUTTE, Belgium—In this small village amid an array of Flemish farms, they were an unusual but seemingly happy pair, two 43-year-olds who were identical, deaf twins. Townspeople recalled seeing Marc and Eddy Verbessem around town frequently, talking animatedly in sign language together, tooling around in a small blue car, and regularly buying two copies of a popular gossip magazine. No one expected them to decide to die on purpose.