[ddsea]

According to [1], "Ded" (literally Grandfather) is used here in the sense of an old man or an ancestor. Snegurochka is his daughter. Ded Moroz's mother was Baba Yaga, and his wife was the Snow Queen. Hope this clears everything up.

[1] https://cb-rzhev.blogspot.com/2013/11/blog-post_4347.html