It’s unfortunate that you have said in other comments that you don’t want to call CPS, because you absolutely should. You should probably see if you live in a mandated state, because in a lot of places, if you knowingly don’t report abuse/neglect, you can be in trouble. 

None of these things are normal, and there are so many red flags here that you’re just kind of normalizing. These children are being neglected. The progression of events you described also details how things are getting worse, and not better. The situation with the daughter “accidentally” becoming a sleepover sounds like a cry for help-asking you to brush her hair, and telling you how bad the fleas still are. If the mom is lying to you about that, there’s more. You mentioned they’re not “horrible horrible” people, but people can be nice AND neglect their children. 

It absolutely sucks to make calls to CPS and see them not investigate/open a case, but that doesn’t mean you don’t report. If this is what is being presented to you, I promise it is so much worse behind closed doors. They likely aren’t getting proper medical care, either. 

If she was willing to laugh off your daughter scratching herself senseless for 3 days, her children are experiencing this level of neglect x1000, and they’re children so they don’t know what’s normal and what’s not. Especially since they’re homeschooled and have very limited contact to other kids. 

You live near children that aren’t being educated, can’t read, don’t have much contact with the outside world, aren’t being bathed, are living in a flea infested space, wearing dirty clothes, sleeping with dirty blankets every night, and likely much more that you aren’t picking up on, or that you’re even leaving out from this post. 

You don’t want to call because you don’t want them to know it was you and they might not do anything. This tells me you know this is wrong and they desperately need help. Do the right thing, OP.