The main criteria is-

1)For Undergraduate-Passed 12th with Mathematics, Physics, Chemistry as three or four subjects of the study prescribed under part III or any other examination of any university or authority accepted by the syndicate of the Anna University as equivalent.

2)For Postgraduate-Undergraduate in relevant subject from a recognized university with at least 6.5 CGPA.

No you do not have to be a good IITian for scholarship but try to be merit in order to get more scholarship benefits. Some scholarships available are BC/MBC,Chief minister scholarship for SC/ST,Merit cum Means Minority Scholarship

For more details you can visit - https://www.careers360.com/colleges/madras-institute-of-technology-chennai