Does your husband really think that there will be a teacher standing in front of her desk at public school?? That happens in HOMESCHOOL! Perhaps you could try reorganizing the families learning, since you have found that your latest scenario didn't work well for you.
I don't know much about other curriculums (my oldest is just in kindergarten), but the way My Father's World is set up, after 2nd grade there is a family circle-type deal, where you would only have one lesson to "teach" each day, and each of your girls would do grade-appropriate work based on the lesson. I. E.- your 3rd grader would have more basic work, where your 7th grader's work would be a little more in depth. This might make it easier to all pile up in the living room for school. They could all offer each other support and help as well, since they would all be familiar with the material. Then they would probably not need you as much for basic questions and the like.
I have a 12 year old son with ADHD, and I fully believe that public school was where I went wrong for him. He did not have the real guidance and supervision he needed; instead he was just tossed in with the rest, and then stayed in trouble for "acting up." He is always bored, disorganized, and hates school. In fact, he has become despondent and shows a total apathy for his studies now, and he has always been an A+ student in his sleep. He lives with his dad now, tho, so not much I can do now
Not homeschooling him is a regret I will live with for the rest of my life.
You and you husband may need to sit down one evening without the kids and come up with a purpose statement for your family and see where and how education fits into it. I hope you get it figured out soon. PM me if you wanna know more of my experience. I'm happy to share.