Take the boxes and leave them on his front porch. Done. Ignore all BS texts and communication about it.
I thought my XAH was never going to get his stuff out of my garage. So...I told him he had 30 days or I would call a local group to come get it for donation. He waited until the very last day, but he did it. Now, that was a whole garage full of stuff.
He still calls me 4 YEARS LATER saying I kept his stuff or threw it away. Mind you, I went out of town and gave him access to the house to take whatever he wanted. For the whole weekend. I have to remind him of that when he accuses me of not giving him all his stuff. Goodness. Reality, he is a mess and cannot keep track of anything and his memory is terrible b/c he has pickled his brain in RX drugs and alcohol.