A Toxic Ex

What is the best way to deal with a toxic ex who lies a lot and tells the children the school, the government, and their mother are not trustworthy? My oldest is sick of being stuck in the middle but still uses him to not go to school regularly and get off chores and other responsibilities. (ex.: After being 3 hours late for school, she will tell me: if you take TV away, I will go to dad's.)