Just to be clear, I understand that you said you've been distancing and detaching from him over the last while.

Do you understand that kind of behaviour can APPEAR to be passive-aggressive attempts to manipulate others? That could be how it appears, to D4's dad.

If he thinks you are trying to manipulate him, and it DOES appear that way in your posts, he is very likely going to continue to resist.

Until he feels you are no longer pressuring him... until he feels that you are actually listening to him... and his needs...