If you decide on biostatistics, do note that some PhD programs automatically consider you for the masters program if you get rejected from the PhD. So it's like a 2-for-1 deal. The ones that did last cycle were Minnesota, Columbia, and UCLA (although you'll want to be sure that these programs will still do this). There are probably other programs as well.
You also have a ton of time left to improve your apps. Plenty of time to study and re-take the GRE and improve that quant score. I would focus on this early so you can get it off your back. You can also take real analysis online in the fall. Harvard Extension School, for instance, offers it (they haven't released the courses yet but they always do in the fall, check back here in a month or so https://www.extension.harvard.edu/course-catalog/courses). You won't have the grades back at the time of application but that's ok. Write that you're enrolled in the course in your SOP and let them know that you took it once you decided to pursue a biostat PhD. Then, immediately when grades are released see if you can update your application with the new transcripts. And if you can afford it right now, paying to take this course is well-worth it if it means you can go straight to a Phd rather than Masters then Phd. The cost of a masters + the opportunity cost is several orders magnitude higher than the cost of this one course.