Engineering

Among these colleges I will prefer UPES for you in terms of placements and study. You can check placements on their official websites.

Yes, you may have a chance of getting marine engineering branch. Please participate in the counselling.

JNTUK and AU are very good colleges for mechanical branch
but you don't forget that all are university level colleges and give the best education.

Yes, you will definitely get seat in AU as you get very good rank
so please participate in the counselling conducts by AU from June 4th onwards.
For more information, please visit www.audoa.in.

Friend, there is no chance of getting NITs or IITs. You can get state government colleges or you can go for other private colleges available.

The total academic fee (with out hostel) for above 10000 ranks is 1,08,000/- and they if you are eligible to get fee reimbursement then you get 35000/- fee concession.

COMEDK 2018 College Predictor
Use your COMEDK 2018 rank to see where you can get admission at the link provided below:
See the courses, colleges & rounds you may crack
The result is based on admissions data of COMEDK 2017
Get resources & insights on colleges & courses
https://www.shiksha.com/b-tech/reso

I don't have any idea about IPU.
If your son has 112 marks in JEE having general category, then he might not get any good NITs easily.
He can go for other private colleges.