My father died of cancer five years ago when I was three years old. He left my mother and
me, their only boy. Last year my mother married Mr. Daud. He was a widower and he had
got two children, Andi and Siska. Mr. Daud now becomes my step father. Andi and Siska
become my step brother and step sister. Both of them are older than me. We live happily in
my step father’s house. Now, we are waiting for the birth of my mother’s baby.

What is the relationship between the writer, Andi and Siska?