I wanted to know in Ziyarat Ashura there has been mentioned in 2nd last paragraph "the 1st, 2nd, 3rd and 4th as sent lanaaht.. " who are these 4?"

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
They are
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