On-line Te Reo Māori Dictionary

Ko Margaret te tuakana o Fran.
Margaret is the elder sibling (of the same gender) of Fran.
Family relationships - older sibling of the same sex - tuakana

Ko Moana tōku tuakana.
Moana is my older sister. (spoken by a female)
Family relationships - older sibling of the same sex - tuakana

Ko Margaret tōku tuakana.
Margaret is my older sister.
Family relationships - older sibling of the same sex - tuakana

Ko Fran te teina o Margaret.
Fran is the younger sibling (of the same gender) of Margaret.

Ko Margaret tōku tuahine.
Margaret is my sister. (spoken by a male)

Ko Chantelle te taokete o Margaret.
Chantelle is the sister-in-law of Margaret.