The twins went to the Lucchese family after killing Roy because they bought weed from Casso for years and he knew them. He cut a deal with them, he flat out told them that they had nowhere to go, nobody to trust but him after DeMeo was gone. He said, if they help him kill him he’ll talk to Nino and Paul about them transferring to his family. They saw it as a ticket to membership and they agreed, the rest is history.