Nanahoshi Shizuka

Can someone explain

Nanahoshi gives rudeus a book on summoning named sig's summoning magic, rudeus's child name is also sieg, is it related to him.

If no the who is sig who gave nanahoshi this book

In the last episode, the voice of a schoolgirl was like Nanahoshi Shizuka's sister [Mushoku Tensei 25 Episodes]