Class 11

Hi Indal,
If you want to go for IIT then you will have to give IIT-JEE entrance examination in which you will have to score at-least 300 above out of 360 (JEE Mains) or 366 (JEE Advanced) to get a good college like IIT Mumbai. Further, you have to score at-least 75% in class 12th for being eligible for admission. So, start your preparations from now. Join a good coaching for your preparations. Hope your dream comes true. All the best.

Please don't use the international level books for JEE, It's JEE not the exam of SAT, TOEFL.
You can use normal books to score good.
Most important NCERT Books.
Apart from this, you can use following books:
For physics
D.C. Panday
For Chemsitry
Arihant Books
For Maths
Arihant Books
Apart from this if you want MCQ books, you can use MTG or TMH Books.
All The Best.

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.