The Nava Yogini's in the Bala Tarpanam are attendants to Tripura Sundari.
Each one is a controller of a circuit in the Sri Chakra which correlates to the 9 avaranas.
1. Prakatayogini
2. Guptayogini
3. Guptatarayogini
4. Sampradayayogini
5. Kulottirnayogini
6. Nrgarbhayogini
7. Rahsyayogini
8. Athirahasyayogini
9. Parpartirahsyayogini
I am also attaching a brief document that gives a full-spectrum overview of what is a Yogini. The "Yogini Cult and Temples" which is stated above is an excellent book to learn more about the Yoginis.
hatley-shaman-2019-yogini.pdf