Who's that?
That's cousin.
Who's that?
That's grandfather / grandpa.
Who are they?
They're grandparents.
Who's that?
That's uncle.
Who are they?
They're sisters.
Who'she?
That's grandmother / grandma.
Who's that?
That's aunt.
Who are they?
They're parents.
Who are they?
They're brothers.
Who's that?
That's father / dad.