Hello Khadarvali, 

Look usually it is very difficult to do both of the things simultaneously. However, as you know nothing is impossible, so you can start your coaching initially by reading a newspaper regularly. That is the most important thing that most of the other students ignore. If you couldn't get a newspaper, you still can know current affairs from News channel, Mobile apps or youtube.

Initially, you needn't required to join any coaching institute. As you have four years to complete your B.tech, And you need B.tech degree to apply in CDS, UES navy, SSC navy etc.( excluding NDA). So begin by reading NCERT, GK, MATHS. 

Then in the third or fourth year, you can join any coaching institute if you want. If you join coaching now you might not able to utilize your learning when its most necessary that is after four years. You will eventually forget everything unless you revise it.

Hope you find this information useful. Have a great future ahead.