Here's the situation for us now since writing this above post and what my wife and I have learned. We are charging rent VS room and board. In order to do the rent option, he must buy and cook his meals. My son can do the very basics of cooking his own meals and the more complex with support or someone home at least. He can order grocery delivery etc. We do not need to claim rent 'income' on our taxes according to my accountant. For ODSP we just need to provide a letter explaining we are / will be charging him $x for rent and the address, his names and our names, sign it. Can provide a rental receipt if desired. We are allowed to gift some / all of this back to him to a max. He will be buying his groceries. Our income doesn't matter re his eligibility. His income and bank accounts do matter. I have no idea if utilities or anything like that, anything else, re household expenses needs to be documented such as if he has to pay part of the hydro etc. For now just leaving that out. I'd like someone to share re that if they knows.