Trying To Prevent Uneducated Grandchildren.?

Ok, here it is. I don't know much about how homeschooling works. My stepson has an 8th grade education and his wife is a high school graduate ( I don't know how she slipped through the cracks). Neither of them are very smart and they are attempting to home school their kids because they don't want their kids in "public school" because some members of their church home school. Our grand daughter is 8 years old and unable to do very simple, basic multiplication. Her reading is ok but we feel that her potential will be hampered by her ignorant and stubborn parents. Our grand daughter is very smart and she catches on pretty good but when she asks her mother for help all she gets is scorn and "come on, you know this" when in reality, she doesn't. She has not been properly taught how to solve problems. The curriculum is what ever they can get their hands on that may be used as teaching tools. What can we do? We don't want our grandchildren growing up illiterate and ignorant. Their are four more to teach after her. Her mother has already stated that she is not sure that she will be able to teach what they need to know and that anything beyond division will be a challenge for her to teach. I think our grand daughter should at least know what 3X3 is. But she doesn't. We can not school her because we live too far away for daily contact. Any suggestions, advise, or similarities would be greatly appreciated.