You can redirect conversations that have to do with your brother. You can not put YOUR money toward his keep. And, you can do what they tell me to do in Alanon... keep out of their business.
If your parents are helping/rescuing/enabling your brother, it only becomes your business when the consequences are yours directly.
I didn't understand the part about "rents" - do you own a rental business and brother is now living in a unit rent-free? If so, then it directly effects your business... but if it is between the parents and him, then no.
Edited to add...
Oh.... erk.... my age is showing. "rents" = parents.
I may be slow, but I am not at full-stop, yet!!!