<p>I tend to agree with greenbutton. You say there is a step daughter? Did the uncle divorce their mother to marry her mother? As you said yourself, you really can have no definite knowledge of what went on within the family. He may have abused them or their mother. He may have just walked away from THEM when they were kids. He might be completely innocent and their mother a villain. You just don’t know. The fact that he is a broken old man now may not cut much ice with them, depending on what happened.</p>
<p>I don’t think that there is any way for you to inform them about his condition without sounding judgmental and interfering. I’d suggest that you simply maintain YOUR relationship with him. If you feel compelled to communicate something to them, I would say that you’ve been visiting their father, and would love to get together with them, too.</p>