Keep your eyes on your goal. You are going to have to make sacrifices. It isn't like the last few years of your work and family life, that there has been this huge block of unscheduled time that you just weren't filling with school and study. You have to carve that time out, and that is going to mean that you aren't going to have time to do a lot of other things. Maybe the house isn't going to be as tidy, or you won't spend as much time on hobbies or travel or socializing or TV or whatever. Prioritize your time aggressively. Put people you love up near the top of the list alongside your goals and basic survival. Let everything else fall away toward the bottom. Get really comfortable with all the things you just don't have time to do, reminding yourself that this is temporary, and that someday you will have a chance to do them again.
Science... it isn't hard. There is a lot to learn, but happily, it all makes sense once you start to understand it. It all hangs together, and the more you study it, the more other parts of it will come into focus. There are resources that make it easy and fun to learn. I like the Crash Course (Biology / Chemistry / etc) series on youtube. It is little 10 minute episodes covering the basic concepts in each topic. Just don't get distracted and end up watching a lot of unrelated silliness on youtube. But yeah, basically, anything you are having difficulty getting... there is someone who has posted a lecture about it, or some other educational video. When you feel stuck, ask the internet. It will explain everything.
Last bit of advice. Find your resources now. You have family who will help with the kids? Are they old enough to keep themselves fed and not on fire? Figure out now where you can turn when you really need a quiet evening to study and line that up early. Think about how you can make several days worth of meals and freeze them in advance, or about who can be coaxed into cooking a meal for your family. Think about how to keep your spouse happy and feeling appreciated. Know where you can turn when the going gets rough. This is a long run, not a short race, and it only counts if you get where you are going. Think ahead about how to stay on track.