I’m not sure what your basis is for this thinking, and I am no where near expert enough to contradict you- but my sense is that you are mistaken
What you really need to do is figure out whether astronomy, molecular/cellular biology, or evolutionary biology is what is genuinely most interesting to you- that’s your major.
Getting into a PhD program requires research experience; completing one means 5-6 years of research in that field; and getting a permanent job almost always requires a post-doc or two.
Astrobiology is a very niche field, and there are only about half a dozen grad programs in the US. You need to scour the pages of those programs (NASA is great resource: Courses & Programs | Careers | Astrobiology), looking at the specifics of what research the different researchers at each uni are working on, keeping an eye out for topics that make you think ‘oooh that looks really interesting’'. In the meantime you need to be looking for research opps for next summer (start with the NASA site and the REU site). These will all be very competitive, and the more you understand about what they are looking for the better your odds.
ps, note that the Edi program is based in astro not bio.