In that case, I’d talk with this friend about how to approach this situation. You can give him or her details that you can’t share here, you can get advice in real time about what to do, and you can get support in what is going to be a thankless task. It is entirely possible that you’re going to need to call the authorities, I’m afraid, but I can’t say with such a small amount of information. I can only say that what you’re describing is NOT a typical homeschool situation. Homeschooled children typically do better, not worse, than their peers in formal schools, even if the homeschooling parent does not have a college degree.
You ARE describing a situation that gets more worrisome with each detail you add. This is not about homeschooling, except that homeschooling adds a layer of complexity to the problem. For instance, if this child were in a public school I can almost guarantee you that a teacher would be agonizing about how to approach this situation, too. Don’t try to handle this alone. Get some help, and bless you for wanting to see these children protected.