JEE Main

No, for getting seats in IISC you have to give JEE advance. JEE advance is not allowed in 3rd attempt. So, you can't get admission in IISC.

Some of the good institutes you can try for are
Medicap University, Indore
Ujjain Engineering College, Ujjain
K J Somaiya Institute of Engineering and Information Technology, Sion, Mumbai
UIET - University Institute of Engineering and Technology, Panjab University
C. V. Raman College of Engineering, Bhubaneswar.

Yes, your son will definitely get admission in IEM. For CSE it might be little difficult, you have to wait till the last round. But other streams like ECE, IT, Electrical, Mechanical will be easily available. Also, since 80% seats are allotted through WBJEE rank he can get any stream if his rank is below 4k in WBJEE

Please visit this link. This is college predictor which will help you: https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

Hi Adi, yes, you will get a seat in SASTRA for sure. You should apply for this college and participate in counselling. Go for branches like IT, electronics engineering, electrical engineering etc. You can also predict your other possible colleges here :
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor
Best of luck.

You can get any state private engineering college by this percentile.