a new marriage

If one of your parents marries again, you have a stepmother or stepfather, and you are a stepson or stepdaughter

• He has never been close to his stepmother 
• If your stepmother/father already has children, these are your stepbrothers or stepsisters
  
  If your parent has another child with their new husband or wife, this is your half-brother or half-sister
  
  

These words are not usually used by the members of a family when addressing each other. They might use first names when addressing step parents