After a long discussion, they decided to announce Orion Rosier-Black as heir Black instead of their son, because in case that Sirius found the other Potter boy, the man could use the boy to take control back of the Black family, but since Orion is the son of Regulus and Sirius was sterile, making it impossible that he would have any children, Orion had precedence to be the future Lord Black, because of the family law that a born Black had more inheritence rights over the heirship than a blood adopted Black like the other Potter boy or a distant relative like Draco or Nymphadora. It would ensure that neither Sirius nor Andromeda would have any control over the house Black.