PP again -did not read your latest post, OP.
You sound a little melodramatic, which is not good for your children. Try to stay calm and assess your options.
MCPS has a website where you can plug in your street and obtain your school district. Stay on top of boundary changes.
I'm very sorry to hear about your son's illness. I hope it was a one-time thing.
However, if you cannot move, you have no choice but to use that public school while you get out of debt.
Your 1st grader is verbal, is she not? With the right (positive, can do) attitude from her parents, she will navigate the "jungle" and be able to tell you if anything untoward happens.
I am prepared to bet that the obnoxious principal (which school doesn't have an obnoxious principal on some level? They have to be, to survive the insane parents in this area

) has learned his lesson and is more vigilant. Actually you should ask him what new policies he has put in place. Don't be afraid to be "that" parent.
If you feel your child has a learning, emotional, or other kind of disability and that is why you are afraid of letting her loose in a public school, then request a meeting with the school. They can evaluate her and offer her appropriate accommodations. MCPS has a ton of special services they offer to students with disabilities - I know, because my son uses them.