Thumper

One solution I've used in a similar situation is to come up with a specific time that worked for me and then told the child "come over on x day at y time." and then I sent them home each time they came over before that. Before they left I'd give them a new day/time. If the parents called or asked, I just refer to the above time. It took a couple of weeks, but it worked well in both the cases I used that strategy. In each instance I didn't want to eliminate the child from my house/life but I needed better boundaries.

That kind of control/boundary might also help you let go of wanting to meddle in another family's life. There really is no graceful way to do that.
I can't imagine one single positive outcome of you airing your judgments regarding his child or his parenting style.

If he out right asks you what you'd recommend that would be another matter and even at that it seems like an enormously complicated situation/dynamic from what you've shared. Personally I'd just say that the dynamics between them were not good for anyone and then recommend professional help to sort it out. It isn't going to be an easy fix and the family will need a good family counselor for awhile IMO.