I've seen similar scenarios, where someone welcomes a friend or family in need into their home to help them out temporarily. The guest doesn't live up to the host's expectations of how to treat his home and how much effort he should be making to get back on his feet. The resentment builds, and eventually the host explodes and kicks the guest out. The guest is angry, and instead of being grateful for the time he got in the house, he now resents his erstwhile benefactor. The host's payment for his kindness is a ruined relationship and lots of frustration.

Since it's your BIL, you can't really talk to him, but you need to talk to your sister. Perhaps you should hash it out with your wife first, and get her opinion. Tell your sister how you feel, and lay out some ground rules. Maybe she's willing to chip in for rent, groceries and damages (at the very least damages). She can talk to her husband about your nephew's behavior. You might set an exit date. I allow my relatives to live with me for free for a month, but after that they have to pay rent. I would not let them stay indefinitely without some arrangement for rent or exit strategy.

Whether Dr. Ray gets a job or not is really none of your business. Do not bring that up. That is meddling in your sister's marriage. Only meddle in your sibling's marriages when your sibling opens up to you about it. Otherwise you are forcing your sister to choose between you and the man she married. You can offer to help him find work, but maybe your sister is happy with their arrangement. Probably not, but it's really her business, not yours.

Don't have your good deed turn into a damaged relationship with your sister. You will both regret, and your entire family will hear about it eventually. Decide what you are willing to put up and offer that. Getting mad will only makes things worse.