Goddess

Two
http://www.indiatvnews.com/news/india/know-why-we-celebrate-navratri-twice-in-a-year-21669.html

Four

By the way, there are a total of 4 Navratri festivals in the year, out of which two are considered to be the main ones (Chaitra and Ashwin month). At the same time, there is also two Navratri Gupta Navratri - one in the month of Ashad and the other comes on the bright side of Magh month. The special thing of Gupta Navratris is that in these, ten forms of the mother of the mother are worshiped, not nine.

http://d01e.blogspot.com/search/label/Mahavidyas

https://www.sacred-texts.com/hin/db/bk03ch24.htm

https://www.google.com/search?q=no+of+navratris+in+year

Five
https://en.wikipedia.org/wiki/Navratri