How do i prepare for the interview for their internship? How important is it? Do they place emphasis on your CV or the questionnaire?

Dont prepare, Trilegal is the easiest interview across all T1s.

yep, they came to our college (T2 NLU), took 5 min interviews for everyone, and hired 11+ non-top 10 rank students. Rest easy brother

hired, as in chosen for the internship right? Also how many people had they selected for the interview round?

Don't believe these comments saying it's the easiest, they take non-top 10, etc. If it was so easy, everyone would easily get into the highest-paying firm in the country.
The truth is it depends on your CV. If your CV, rank, credentials, etc. are so good that it speaks for itself, they might wrap the interview in 10 mins with hardly any technical questions. If not, you might get grilled hard. I know people who had intense interviews before they got an offer.

I’m a lateral and more senior to you. It was much easier compared to AZB and Amarchands. Others may have had a different experience.

Definitely not easy.