It’s not clear from our scholars as to who are they. It certainly refer to those who murdered Ahlul bait.
Some are of the view that
1. Qabil who killed his brother Habil
2. Qaidar who killed the she-camel of prophet Salah
3. The killer of prophet Yahya called Malik
4. The killer of Imam Ali
5. The killer of Imam Husein
There are also other opinions. However, as I said it’s not known Certainly. It could be anyone who caused the killing of Ahlul bait