do company like amazon differentiate between branch when it come to college for placements ??
ideally they don’t. I work at amazon and they don’t condone biases regarding literally anything, that includes much more bigger things like gender, religion and many other important aspects, and branch of a candidate is very less important than that. But if you’re unlucky, you may find an interviewer who has personal biases towards branches and may give a negative feedback towards you regardless of your performance (which is extremely rare, but it really depends on an individual). Even after that, the decision is never based only on 1 interviewer, so a candidate being rejected just because of one’s branch is almost impossible (because you really have to be very unlucky to encounter more than 2 interviewers like that 
). But in a general sense, NO, any kind of partial behaviour is not supported by amazon or any other company like that (I assume you mean FAANG companies).
PS: if you ever encounter a situation where you think you were wrongfully rejected, please try to reach out to hiring manager to learn about the reason you were rejected.
can you please tell me is there any procedure to apply offcampus in amazon for internship(3rd year) ??
or any hiring challenge going to conduct ??
You can apply on the job portal at jobs.amazon.com for any position you find suitable, and they usually have hiring challenges on HackerEarth. But I’m not aware of any ongoing drive for interns, they usually happen before winter and summer internships.