For your first question, I don't think school would let you double up on your actual nursing classes/clinicals. As my school puts it, the nursing curriculum builds from simple to complex, so classes must be taken in a specific order/succession. Plus, eeeekkkkssss!!! the thought of two nursing clinical classes!!! The thought almost gives me a heart attack!
As for your second question I would say that if you get along with your parents and THEY wouldn't mind you moving back in, then, I myself would probably do it. After I graduated from college and moved back in with my mum for a couple months before finding an apartment it really wasn't all that bad. I think it was actually easier living with her as an adult than as a child because she respected that I was an adult and gave me more privacy. I think the hard thing was that I didn't have my own stuff. All of my furniture etc. was in storage and I wasn't even staying in my "old room" because she had moved to a new house and I was in the guest bedroom. So, I felt kind of akward for a while.
I don't think you should feel like a "looser" because you are 28 and want to move back in with your parents. I think it is a smart move if you can do it, it will allow you to save money, possibly work less, and not feel so strapped for money or time. Heck, any move you can make to keep down school loans, etc. you should try.
I don't know where it's like where you live, but here in Pittsburgh it is absolutely the worst place to be a person in your 20's because there are absolutely no jobs for new grads and even if you did get a job years ago by now you are probably laid off and can't find another. I know tons of people in our age group (I just turned 28 myself) that have had to move back in with their parents because they don't have a job and no income to be out on their own. Plus, some of my friends have gone back to school and are saving money for tuition and books by living at home.
So, I don't think you should feel bad and you are certainly by no means a Looser.
Good Luck and take care and PS, I have a 92 Ford Taurus that keeps on tickin', I too am concerned about her lasting another 2 years but God willing and by the power of my mechanic I think she'll pull through.