I know from experience what joys and hardships having an adult child at home can cause. Especially the second time around, not to mention third and fourth. I assure you it may hurt their feelings and you may feel like "scum" doing it but it will save you financially, mentally and emotionally. You have to come up with a written agreement, especially if there are wives and significant others involved. They can save money but they need to understand you need some $ for supporting them.
Seriously, you'd actually suggest taking legal action on your own children? That's ridiculous. Try this agreement "Pay me $x per month or I'm telling everyone on Facebook you're 30 and still live with your mom."