Alpha is Beta sister.

Gamma is Beta mother.

Delta is Gamma father.

Sipi is Delta mother.

Then,

How is Alpha related to Delta?

Alpha is the granddaughter of Delta.

Explantion:
Alpha is the sister of Beta and Beta is the daughter of Gamma.
So, Alpha is the daughter of Gamma.
Also, Delta is the father of Gamma.

Therefore, Alpha is the granddaughter of Delta.

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