JEE Main

You may have chances to get Government Institutes, because of decrease in B.Tech admission graph since last year. Apply for several state and JOSSA Counselling also according to eligibility. Go ahead. Good luck.

Actually, in Sastra University, they won't consider B.Arch marks in admission process. Basically, for getting into Sastra University, there are two processes.
Stream 1: which is JEE + inter marks
Stream 2: only inter marks.
For your son, considering the given data, getting seat is difficult. There is no donation seats. But, some seats are available in NRI quota and NRI sponsored quota.

Hello David,
I am afraid the date for filling up application forms for the appreciation of JEE Mains examination is now over. As the examination is being conducted in the month of April in multiple sessions I am doubtful if National testing agency will extend the final date of application. I think you are missed the bus for April examination. Best wishes.

Yes, you will get the final rank online. The ranks will be based on the two examination of JEE. The rank will be based upon the best score and everyone will get a rank irrespective of the number of times he has appeared. i.e. January and April.

Yes, you will get a seat here with a scholarship. You can easily get the merit cum means scholarship. By the way with such a percentile admission is sure, apply in JOSA portal.

The final AIR will be declared after April 2019 considering the best score out of the two JEE Main attempts for all the applicants, hence based on current percentile we cannot predict for which NIT you will qualify. Wait for the final AIR declaration
Details:
https://www.shiksha.com/b-tech/articles/how-to-calculate-jee-main-rank-from-percentile-blogId-19953.

If you get less than 75% in class 12th, you are not eligible for IIT. But, you can get NIT with that percentile.

It is a little bit difficult to get your seat in the desired college with this percentile. So, just give a try in the counselling.

It is a little bit difficult to get a seat in your desired college because of heavy competition. All the best for your future!

Being an OBC student aiming for NIT Patna. I can say, you hold a chance of getting a seat into it.
Good luck
All the best