Class 11

First examine yourselves by giving the aptitude tests and then decide because it is all about your passion and interest and most importantly don't try to take your decisions based on your friend's advice.

You don't think you are quite late asking this. You should do class 12th and 11th course together. Means in day time either do class 12th and at night class 11th and vice versa. For IIT during doing class 11th and 12th course do questions for IIT too. By this you will be able to score good in IIT too.

He can get an institute admission for Diploma not Bachelors as the eligibility:
Diploma Class 10th pass from a recognised board with minimum 40% marks.
Bachelor's Degree: Class 10+2 examination with at least 50% marks.

You can pursue a Diploma as Diploma Class 10th pass from a recognised board with minimum 40% marks.
For a Bachelor's Degree: Class 10+2 examination with at least 50% marks.

As you are still not sure about your career option between engineering or medical, you are advised to select PCMB subjects in class 11th and 12th.

The fee structure depends from college to college. Colleges providing the best infrastructure and good amount of facilities will demand more fees as compared to that of the other colleges providing low infrastructure facilities.

Hi Sukruth,
Migration Certificate is totally in the hands of the school authorities. You will have to request your school personally to provide you with same. Such cases are in discretion with the school/college's very own decisions. Kindly contact your administrative block as soon as possible.
All the best.