Omega's are far sought after, some even being stolen from their homes. So when Kim Seokjin's family find out he's an Omega, they being him up as if he was a BETA, feigning sickness to feed him suppressants. Kim Namjoon's sense of smell has never gotten it wrong and he was dead set in believing it wasn't wrong this time either. Kim Seokjin is an Omega, no matter how the man tries to convince him otherwise. And it isn't just him that knows it. He and his five brothers-by-choice feel it. Kim Seokjin is their Omega.