Relative clauses. What time should I use? (Point of action?)

I have a sentence. I’m not sure if it’s correct, but I have to ask. I know theory about reffering to the previous clause, but I don’t know how it works here.
What I think:
a) I saw an article about guys who had been driving car while listening to their favourite artist, and who had had a car accident because of that
b) I saw an article about guys who had been driving car while listening to their favourite artist, and who had a car accident because of that

So I have a problem.
In "a" I assume that "who – clause" and "and who – clause" are subordinate to "I saw an article about guys", do in both parts I have to use past Perfect because it happened before "I saw an article about guys"
In "b" I assume that "who – clause" is subordinate to "I saw an article about guys", and "and-who clause" is subordinate to "who-clause", so I have to use in "who-clause" past Perfect because it happened before "I saw…", and I have to use past Simple in "and-who clause" because it happened simultaneously with "who-clause".
Can someone explain me that?