The question should be is it possible for "you" to do well. I took Honors Ochem and Physics, along with two other lab science classes in back-to-back semesters. I also worked three part-time jobs at the same time, and did 8 hours of volunteer work a week at the ER and taught an occasional CPR/First Aid class for American Red Cross. I made A's in everything and still had time to hang out and relax a little without seriously damaging my personal relationships.
So... it was very doable for me.
Is it doable for you?
That all depends on how much work you put into it, what kind of professors you get, how motivated you are to succeed, how able you are to sacrafice a good night out for studying when you need it... the list goes on forever.
There are two choices you can make. One, do one at a time and insure yourself of a relally high grade without having to work too hard. Two, challenge yourself, take on the classes like a challenge and prove that you are willing and able to get the job done.
The one that will help you in the long run is to take on every challenge and mow through it like a chainsaw through warm butter. If you don't challenge yourself now, you may find that you can't cut it when it comes to medical school. The classes in medical school really are easier than some of the ones you will take in undergrad, but you will need to learn them all, and at the speed of light too, in order to do well. There is NO amount of work you do in undergrad that will ever amount to what you do in medical school, but challenging your mind now and shaping your attitude into an "I can do anything I want" instead of an "I wonder if I can do this well enough" will be highly beneficial for you.