Explain the difference between your immediate family and your extended family
Your immediate family are your parents, children, siblings. Your extended family is anyone related to you who is not your immediate family (ex: cousins, uncles)
Explain the difference between brothers/sisters and siblings
"Brothers and sisters" and "siblings" mean the same thing, but sibling is more formal and is used for both genders.
Explain the difference between an adopted child and an only child
An adopted child is one who has become part of a family which is not the one in which he/she was born. An only child is a child who doesn't have siblings.
Explain the difference between a brother and a brother-in-law
A brother-in-law is the the brother of your husband or wife, or your sister's husband.
Explain the difference between a mother and a stepmother
A stepmother is married to your father, but she isn't your biological mother.
Explain the difference between a stepsister and a half-sister
A stepsister is the daughter of your stepmother/father and their previous husband/wife. She isn't related to you. A half-sister shares one parent with you.
Explain the difference between a father and a parent
A father is the male parent of a child. A parent is the mother or the father.
Explain the difference between a grandfather and a great-grandfather
A grandfather is your father/mother's father. A great-grandfather is your your father/mother's grandfather.