I have been through this from both angles...as a sister first (my sis and I are less than 1 year apart) and as a mother of two girls.
My sister and I switched between rivals and best friends as our mood struck. As we got older, we really began to celebrate our differences and not try to step into each other's limelight. She is an incredible athlete and I am more musically inclined, so I left the sports to her and she left the music stuff to me for the most part. The unfortunate thing for my sister is that my family definitely values music more than athleticism, which they have unintentionally voiced from time to time. So that is my first bit of advice to you...if they do choose different types of hobbies than each other, be sure to praise them equally for their accomplishments within that activity regardless of which hobby you value more.
Now, as a mother, I highly recommend two things to help your 2 year old with the transition before the baby comes. First, spend some time with Amelia showing her photos of when you were pregnant with her and when you went to the hospital to have her, including early pictures of her as a baby. This will help her to understand the fact that the baby you have inside you right now will be coming out for good once you go to the hospital to have her. I did this with my oldest daughter (who was also just over two years old when her sister was born last December). She loved seeing the pictures and hearing the stories about when she was born and I do believe it made it easier for her when the baby came. Second, get her a "Big Sister" book to read to her and play up the whole big sister angle. I looked around at the time for a decent big sister book and ended up with "I'm a Big Sister" by Joanna Cole, which she really enjoyed hearing.
Once the baby comes, be sure to spend what special time you can with Amelia to make sure that she knows she hasn't been replaced and that she is still important. If you can, read stories to her while the baby is nursing or taking her bottle. If that doesn't work, then sit and have quiet snuggling/reading time with Amelia as soon as you put the baby down for her nap. It's difficult juggling the needs of two small children, but taking a little bit of special time aside for each of them (especially the toddler while the baby is too young to know any better!) will make the rest of the day go smoother.
Good luck!