L.R.
Yep, tell your husband you are a business owner and must give your business your attention. Then put your daughter in a preschool. He does not understand that preschool is about much more than learning a few ABC and 123s that he thinks you should be able to cram into your day; it's actually MUCH more about social skills; learning to follow directions; learning to stop one activity and move to a different one when asked; and learning to do all these things when directed by a person who is NOT your parents. These are vital skills for being ready for kindergarten. You can't provide all that even if you want to, because you are running a business with younger children who require your attention.
Your husband, by the way, should be doing homework with your son at least some of the time--maybe most of the time; he should help you visit and look into local preschools for your daughter; and he should stop the "You're home, you have time to do this" attitude. I'm sure he means well but he has no real idea of what you have to do all day, does he?