Ahhh, medical school interviews... Good times. XD I've been through my fair share of med interviews as well and admittedly, it CAN and WILL be a daunting process for the uninitiated.
Here are a few general tips I've learned along my way.
Note: They may not be the best tips available but the feedback I received from my interviewers was very positive so yea, whatever goes.
1. For ethical questions, as you said, it would be useful to put both sides of the argument into it. However, try not to present yourself as a fence-sitter. The interviewers are looking for fluent, articulate and well-spoken candidates so obviously , they will grill you a fair bit when required to do so.
Hence, try to be firm on a stand that you believe in and make sure you have solid reasons to back them up. The wonderful thing about ethics is that as long as you base your arguments around ethical principles, you can never be proven wrong (or right).
2. Rehearsing answers to common and expected questions would be a good way to prepare for the interviews. Questions like "Why do you want to be a doctor?" and "Tell us about your personal traits that you think would make you a good doctor" come to mind.
AVOID GENERIC ANSWERS.
Things like "I want to be a doctor because I like to help people" will only raise eyebrows. Even if the generic answers reflect how you feel, try to add a bit of flair and personality into your statements. Think about them deeply and try to pull the words out of your heart.
As an illustration, here are some generic answers in comparison to similar but more meaningful ones:
I want to help people - Medicine attracted me because it's one of the only professions where you can have a direct impact on the lives of others. Not many jobs give you the privilege of connecting with others at such deep emotional and psychological levels.
I think I'm able to handle the course - Medicine is intellectually challenging and I feel that I can learn a lot academically and holistically from the course.
Things like that.
I know it seems very dramatized and all but trust me, take 10 minutes to sit down and think about it... You'll be amazed at what your inner self tells you.
3. As a final point, a medical interview should not be treated as a barrier or hindrance. Instead, think of it as an opportunity to let the interviewers know about you and to show them how much you're worth. Hence, try and be yourself as much as possible.
Remember, you are merely human and the interviewers know and expect that. It is not a complete disaster to screw up a little, nor is it wrong to be brutally honest about a shortcoming you have nor is it wrong to say "I'll have to be honest and say I'm not too sure about that. Sorry" to a question you don't know how to answer. In fact, it may even give you some extra points; humility, honesty and self-awareness are commendable traits to have.