Ответ:

  1. Beth is your mum. She’s your dad’s wife.
  2. Your father’s sister is your aunt.
  3. Your sister’s daughter is your niece.
  4. The son of your daughter is your grandson.
  5. Your uncle’s son is your cousin.
  6. Your wife’s mother is your mother-in-law.
  7. The mother of your father’s father is your great-grandmother.
  8. Your parents are divorced and your mother is married again. Her new husband is your stepfather.

The two unused words are father-in-law and grandmother.