So first off, I understand the frustration you feel for your friends, and it seems you are writing out of concern for their wellbeing that their adult children are putting on them. That is admirable - you are a caring friend.

As to your question, what can you do? Nothing. And nothing is pretty much what you should do. You cannot save these adult children or save their parents from them. You are already doing exactly what you can: offering appropriately tempered advice and offers of assistance (resume reviewing, etc.) but ultimately you cannot force them to do anything.

As a friend, the best you can do is offer moral support to your friends as parents and you can keep offering to help review things or provide advice. Other than that, it's the parents' job to push those kids out of the nest and let them figure out how to fly. I know that's harsh, and also it's a lot harder for kids to start out in this day and age, but it's not going to get any easier. But, like I said, it's not your place to do any more than what you are doing.

And thank you for being a good friend. I'm sure your friends appreciate how thoughtful and caring you are.