I'm not a nurse, I'm a Respiratory Therapist, but maybe I can help you a little. The hospital is its own little world, and it's not for everyone. It can be very intimidating, and it can be extremely stressful as you hold people's lives in your hands. If your gut is telling you that this is not the kind of stress you want to live with, and you have the option of finishing a different degree, I'd say go for it! The nursing school you've already had will never be wasted. You've got some background that will help you with your own kids, and maybe even your future students if you go for that teaching degree.
If you go forward with nursing, you'll be hard pressed to find a job where you never have to work weekends or holidays. That's just a given. The hospital has to be staffed at all times. If people would just figure out that they should only get sick M-F between 9 and 5, and that after surgery they need to get out of there before the weekend...
It's the nature of the business.
My husband is a teacher, and I hope you don't feel like that's a lesser profession than nursing. We need more nurses, but we also need more good teachers! Teaching is a great job, and as you know, you'll have similar hours to your own kids. You don't get a whole three months off during the summer, like they do, but you'll get about two months. Even though you've always wanted to be a L&D nurse, there's no reason why your dream can't change. L&D can be very stressful. One bad baby (I don't mean he doesn't behave; I mean those tiny ones who have major medical problems) can put your stress bar at a whole new level. It sounds like you're halfway to the decision already.
One last thought: nursing is hard on your body. You don't see many older nurses in the hospital. It's just too hard. But you can teach until you're ready to retire!
I wish you the best as you make this important decision. Do what's good for you and your family for the long term!