Greetings!

Respected sir/madam, the cutoff of Amrita is fairly high, for CSE in main campus you can expect it to hover around 96-97 percentile, so that is going to be very difficult to get. However you can get into core branches in Amrita.

Now coming to VIT/SRM

Neither of SRM and VIT accepts, both of them conduct their separate exams, SRMJEE and VITEEE respectively. However if someone is able to get 93+ percentile in mains, he is expected to clear them and secure admission without much difficulty, but if your son hasn't appeared for them there isn't anything that can be done about it right now. So maybe you should try to find the best college you can get into, and for that you can use the following tool

https://engineering.careers360.com/jee-main-college-predictor?utm_source=qna&utm_medium=jee_cp

~Sach Thadani