Pls suggest iam very confused about my son ,he is not getting any good rank in any btech entrance exams but he wants to take long term for

First of all, Don't stress up yourselves as well as your son. Take a light mind and then think about it. Is IIT and NIT all that is there in B tech? If yes, and you are willing to take a year drop to prepare then well and good. You should prepare your mind to do the hard work that is needed as it ain't going to be easy. For coaching institutes in Hyderabad, Sri Chaitanya have built a name for themselves in that region else you can go for REsonance or Allen, but all these won't matter until the effort is taken from your side.

Good Luck!