What if I fail in 2 subjects in ICSE Class 9??

Nothing will happen. ICSE calculates the best of five subjects out of 6 and if someone is fail in one subject it will not get calculated. Your percentage will come out of 5 best subjects,so need to worry. Remember that English is the Compulsory subject and you have to calculate best of other 4.
https://www.ribblu.com/cbse/papers/class-9