what happens if we fail a unit, do we get kicked out, or do we repeat the subject?
Essentially, nothing.
If you fail more than 50% (or might be exactly 50, so, 2 units) of your units in a semester, they send you a "warning/reminder letter". Saying it might be a good idea to come down and talk to someone. Nothing else happens, you dont even need to talk to someone.
If you fail more than (or equal to, cant remember) 50% of your enrollment across two concurrent semesters, you might be referred to an academic progress committee. It is a little scary, its a panel of a few academics and a student representative. You're even allowed to have a lawyer if you like as far as i know. They use different committees for all kinds of things, sometimes, they deal with serious stuff like harassment, stalking and plagiarism, so, failing a few units is nothing in comparison, even if you do have to see them, compared to these other situations, its nothing. You have to explain (if you choose to show up) why you think you failed, they discuss with you how to fix it. It might include checking in with a mentor weekly, seeing the counsellor, etc.
Usually, they wont throw you out for failing, even if you do come before the committee, especially for a first timer. If despite all their advice you don't listen to them (visit the counsellor, see a mentor, reduce your study load, etc) and keep failing, *THEN* you might be in some shit. By that point though, things have gotten out of hand to the extreme.
TL;DR A surprising amount of people fail units, its nothing to be concerned about. If you start failing half your subjects every semester, for a few semesters, then you might need to be worried but you're no where near that.