Prahlad Progeny

1. Virocana was the son of Prahlada and
2. Mahabali was the son of Virocana.
3. Bana was born from Mahabali and
4. Four crores of Asuras called Nivatakavacas were born from Bana.

https://freeglobaluniversity.blogspot.com/search/label/Feet

Nivatakavacas With Ravana (of Ramayana) and Arjuna (of Mahabharat)

http://en.wikipedia.org/wiki/Nivatakavacha

Source (Agni Purana, Chapter 19)

1. Virocana was the daughter of Prahlada married to Tvastar son of Shukracharya 
2. Trisiras and Vritasura were Sons .

https://en.wikipedia.org/wiki/Tvastar

1. https://en.wikipedia.org/wiki/Trisiras
2. https://en.wikipedia.org/wiki/Vritra

https://www.sacred-texts.com/hin/db/bk06ch01.htm

1. After death of his above two Sons by Treachery 
2. Tvastar Cursed Indra for Life worse than Death

https://www.sacred-texts.com/hin/db/bk06ch07.htm