hello,

yes you can join through LEET for engineering course. If you want to go IIT then you have to go through all the 4 years. You won't get admission from 2nd year.  for joining IIT, you have to clear jee advance with good scores and for JEE Advance you have to score good in jee mains.

The answer is yes but not from second year but from 1st year. It is a highly competitive exam so prepare accordingly and score well in the exam. Practice hard and make yourself shine.

Hope it helps!