Anyone have any research on adult kids with undiagnosed ADHD parents?

My friends are 28 and 32. I had dinner with their 67 year old dad last week. I'm no doctor, but this guy fits many of the symptoms of ADHD. I've been reading this sub for two years, he got my spidy-senses up.

The clincher besides his behavior at dinner, are what my friends told me. He hords stuff, they have two storage units and that is down from four. He also can't leave food, or let anyone leave their plate or glass empty - it's compulsive, he becomes automaton about it. I'm thinking about co-morbidity issues here. There is other stuff, I won't go into.

My question is what kinds of issues should his kids (my friends) be addressing in their own health? Specifically, both of them have crippling anxiety, control issues, and sometimes what looks like OCD. Neither seem to have ADHD (to me). What is nature vs. nurture here? Could they have inherited just the comorbid type traits without the ADHD?

Edit Thanks everyone for your help. The man in question died two days ago. I am now more occupied with helping my grieving friends cope.