You sound very much like my mother: She was a SAHM for about a decade, and when my dad left we were in a mess. Her job skills were rusty, and she wasn't able to get anything except a very basic service job -- like you, she went back to school, and then she was immediately raising us on an entry-level salary. As the oldest child, much of the childcare, cooking, and cleaning fell to me. Those weren't good years.
I think your plan to begin work, move into an RV, and homeschool while working is overly ambitious. You only have 24 hours in a day, and you'll burn out sooner rather than later.
I don't think the RV will be enough space for three children to play and for you to work. Even for minimalists. You'll need quiet and the ability to focus on your client's needs -- or you won't have clients for long. It's unrealistic to think that young kids will sit quietly and do their schoolwork while you're working a full day. You can't be on the phone with a client while Sponge Bob plays in the background or the children are loud (or even just talking normally).
I think traditional school is your best bet. Homeschooling, when done well, can be a great thing, but it's a full-time job and requires significant resources -- the biggest resource of all being time. I don't see a person in your shoes being able to do it well. You've been a SAHM for a while -- do you have experience in a professional job? I wonder if you're underestimating the effort it requires, especially when you're new and are learning the ropes.
Why is your situation with your parents about to end? Would they allow you to stay with them perhaps another year, while you begin your career? It seems to me that stability -- especially for special needs kids -- would be good in a time of transition (adjusting to you working, adjusting to the oldest going to school).
