Here are some ideas if they don't do all their work. That's really all it takes. But, you have to stick with it. That's the hard part. You can't say, you're grounded this weekend, and then bend when they beg all sweetly.
Consistency is definitely the hardest part.
I hope these suggestions help. Please email me personally anytime you need a shoulder to lean on. Unschooling requires the same thing. We unschool our 10y-o daughter. She decides the subjects she is interested in pursuing.