In order to get these colleges you have to appear for JEE Main and you have to apply for TNEA exam.

To check the cut of SSN college you can refer below link

SSN Cut Off

Sastra takes admission in two ways-

In stream 1, 70% of seats are allocated.
In stream 2, 30% of seats are allocated.

Stream 1:
In this stream, both JEE Main marks and 12th Board marks will be considered, where 25%weightage is for JEE Main score and 75% weightage is for Board marks. 

Stream 2:
This is purely based on your 12th standard marks. And your normalized 12th board marks score will be taken to eliminate partiality between State, Central and International boards. 

You should score 95% marks in boards class to get Sastra in Stream 2.

Can you please tell me full name of the college NTU?