Unpaid high school tuition

My ex-husband insisted my sons go to private schools. Now he refuses to pay their unpaid tuition. They can not go to college because they have no transcripts because he has not and refuses to pay their remaining tuition. He signed the financial agreement because I could not afford this. The school is sueing him for this amount because he signed the financial agreement. How can I take care of this? His only advice is for my sons, ages 19 years and 17 years, to get a job and pay it off. If he can not afford it working full time how could my children possibly afford to pay this off? THEN....figure out a WAY TO GO TO COLLEGE??? He is, as you can see, a real winner. Thanks for any input! Up a creek in Nashville.