The BA is a perfectly good degree but it probably has fewer required upper division technical courses. It may be possible for you to take some of those as free electives though. As for being able to make it in Astronomy or Biology, I have found that success depends mostly on the amount of effort you put into the things you study. If you can get As in STEM courses, then you can learn. That is not measured by the AP and SAT tests.
Finally, for your question about a double degree, I suggest that you start with one and then see in your first year if you want to go for both. Astronomy and Biology are far enough apart that it might take you extra time to complete the second degree. You also have to consider if you are interested in eventually getting an advanced degree in Astronomy you don’t really want to spend extra time on Biology courses but take all the physics and Astronomy you can and find a way to get a lot of research experience.