They must have had at least 3 (three) years of education in any Foreign country during the last 6 (six) years and must pass the qualifying examination (inclusive of 11th and 12th standard or equivalent) from abroad only.
Student who has studied 5 years including 11th and 12th in abroad then he is also called NRI student. If the Student studies till 10th in abroad and studies his 11th and 12th in India, then also he is not eligible for entrance exams under normal category.
Most of the reputed institutions take advance booking, it will be better that NRI post their request for information about admission options, scope and duration of a course, admission procedures and timings of various schools and colleges in India, sooner than later.