At least for me, deciding what to do was a long series of trial and error. I first identified careers that were interesting that I thought I would enjoy, then culled things that wouldn't fit with what I perceived as my lifestyle requirements (often something that often changes a lot for peope as they go from HS to college and college to workplace). I then took the careers I had left, talked to people in those fields, took related classes in college, read stuff on the internet. Pretty much used every resource available to confirm if I would like the field or not. I came up with two things I really liked (medicine and economics/finance) and then I continued exploring those two until I thougth I had come to a solid conclusion of what I wanted to do.
That paragraph makes it look easier than it is. The above has taken me over seven years, and once I thought I had it all figured out I got a job offer that forced me to seriously consider switching. What I'm trying to say is it's ok to be uncertain, until you actually get going in X field you can never truly be 100% sure if you'll like it or not. The goal of course is to try and get as close to 100% sure as you can.
You have lots of time to decide what to do, there's no rush. I'd recommend talking to teachers and pharmacists (maybe ask your sister?) to see what the jobs entail. SDN is a great resource for health careers, I'd recommend reading through some of the pharmacy stuff. You may find yourself like me where you have trouble deciding, but the decision could also end up being easy for you. There's a good chance you'll find yourself in career other than the two you mentioned. College offers a chance to explore all kinds of subject matter, when you get there, I recommend taking advantage of it.
As for doing what your parents want, it's great to have your parents happy with you, but it's more important that you be happy. I know a number of people who's parents pushed them into X career or X school, and a good portion of them transfering schools or switching majors in their last year(which then makes it not their last year). I'm not saying to discount your parents opinons, they are older and most likely wiser and thus may have some good insight. However, don't do anything just because they want it, they may just be comfortable with that college due to your sister being there. When it comes down to it, you have to live the life you choose, so make sure you try and choose one that makes you happy. Assuming you have a healthy relationship your parents, they will accept and be supportive of you no matter what college you attend or what career you choose.