Taking classes

Without knowing your personal circumstances, I'd say that your original plan is obtainable. However, getting into nursing school isn't a race and do what you have to do to learn as much as you can before getting into nursing school. For instance, this summer I'm taking a 4 week A&P 1 class and a 6 week A&P 2 class back to back, just to make sure I can get into the nursing program on time. Whatever you have to do to reach your goals.

I'm a stick in the mud, because I just don't think the important science classes should be smooshed into the summer. I had to put my application on hold for a semester - it sucked, but it's what I had to do to make sure that I had the solid foundation I needed. I'm finishing up my first semester of nursing school now :)

This is all my opinion of course. You're free to do as a choose.

I personally think it is attainable, especially if you already have good study habits and time management skills and don't have to work full time.

While I took my A&P2 and Micro in a fall semester together (and got A's), I did take my first A&P in the summer, all while working full time. I didn't have an issue getting an A and learning the material.

This is completely dependent on the type of student you are. Personally, I don't like the idea of squishing sciences into summers and definitely not when doing two sciences at once. Micro and A&P's are bit more challenging than the average science class. I wouldn't risk rushing it because I know that while I'd likely pass, will I be able to swing an A and be competitive as an applicant? If you know you're the type of student who has the aptitude to make that happen I say go for it, otherwise I'd take it slow and steady. Good luck either way.