Ehhh, your looking at this wrong. They've actually found the answer: disconnect. Society and societal success is a soul sucking pursuit that leads to early death and misery.

That dosen't mean they don't need to earn their keep. Let them do what they want, but don't let them take advantage of you or your good graces. Charge them rent. They should be buying their own food, etc. If you don't want them living with you, perhaps they can move out and get a place together.

You're making it too comfortable for them, and that's causing more harm than good. People just go from womb to womb. It's part of our nature.