To be honest I would speak to the nursing departments about their specific programs and what they recommend. Each program is different. For example, the one I'm applying to gives 40 points for As (first time), 30 points for Bs (first time), and then the second time around gives 20 points for As and 10 points for Bs. So based on my program you'd be safer to stay with your Bs. However, other programs I know you NEED an A to even be competitive and it would be worth it to take the class over again. Like I said, talk to the specific nursing departments for what they recommend for their programs.
As for finding a teacher that wouldn't be terrible, ask around if you have the chance. It's easy if you know people that went to the school or program. If you don't know, perhaps ask an advisor for the program if they could perhaps put you in touch with a current or former student that might be willing to answer questions. Also, if it's a local school see if any of your neighbors, coworkers, relatives etc. are familiar with the program. I also check the ratemyprofessors site, but I do have to say: take those reviews with a grain of salt. You don't know what type of student the reviewer was. They might have been a poor student and gave a bad review because they received a poor grade. You never know. I use it as kind of a guideline. But best bet is to try and talk to somebody.
I noticed you said that you work 40 hours a week. Are you also taking a full load of courses or only one or two at a time? I'd recommend either that you cut back on a few hours at work (if you're able to) or take one or two courses at a time so you can focus more energy on the classes. That may help with grades.
Best of luck to you in this process. It's a lot of work and energy, but remember: where there's a will, there's a way.