If I were you, I would definitely START nursing school while you are still at home... but continue to have/attempt to have kids as "planned".
There are plenty of nursing courses that you can take online... and most schools that I know of offer online courses. Don't overload yourself, but take the general education courses that are required at home, and then when your kids are going into school... take advantage of that time to get your hands on classes and clinicals done.
My SIL has 3 boys and she took online nursing courses and held a full time job and it is a LOT of work and scheduling. You can do it, but unless you really NEED to become a nurse soon (financially) then I would take your time. Your kids will only be babies for a few years... if you had each one "about" 2 years apart, sure you may have to wait 10-11 years total before they are all in school full-time (elementary and up) - but you are only 3 years or so from your 2 year old entering kindergarten... right now you could probably take on a class or two online and get it out of the way, while still staying at home with your two. It might be a challenge, but isn't that what being a mom is all about? If you took 2 courses every semester, that is 4 per year... in 5 years you could have 20 courses done!
by the time your kids are all in school you could be 50% or more done with nursing school, all from home... and then you could go to school full time and be done in a year or two, while not having to wait a long time to have your kids.. which are an 18 year 24/7 commitment per piece.... at minimum.
Of course you could wait till they are all in school to even start... but then you will have to spend the full amount of your time in school full time, and it will coincide at some point with your oldest in high school, which may become overwhelming as you prepare for her and then her sister to leave the nest. It might be nice to be done, or at least almost done with YOUR bulk of school before your kids are out of middle school.
Of course, no matter what you do- there will be challenges! Good Luck no matter what!
-M.