About Rox and Lana Flashback and Quinn's story :
In Ep 6 we see a flashback from Quinn's POV :
Jonathan and likely Lana buy the (laced) cocaine which then kills Lana.
On the mattress lies an unconscious woman, according to Rox' comment likely Quinn's mother.
Rox consumes cocaine.
The scene matches with the Ep 11 Lana flashback.
If mc is on the "Others" path and has good relations with Quinn, in Ep 11 she will tell the story of Rox' death :
qu "When Dad died, I was seven years old."
qu "I went to bed early but couldn't sleep, so I got up to check what he was doing."
qu "Mom was passed out on the floor from drugs and Dad was snorting coke with Buddy."
qu "Dad caught me peeking at them and knew what I had seen him do."
qu "Even at that age, I knew what he was doing. I grew up around him selling drugs, but he tried not to use them in front of me. It was his way of protecting me."
qu "Buddy told me to get back into bed. He called me a rat and Dad snapped at him."
qu "He screamed and threatened Buddy by holding a knife to his face."
qu "I was shocked because I had never seen him be that mad at Buddy."
qu "Shortly thereafter... Dad had to sit down because he didn't feel good. He couldn't breathe..."
qu "He...missed the chair and fell down on the floor."
qu "He started convulsing... Foam...like bubbles in a bath, erupted from his mouth and nose."
qu "Buddy was panicking and didn't know what to do."
qu "He screamed at Mom, kicked her and tried to wake her up and help."
qu "But that drugged-up bitch was dozed off as if nothing was happening right next to her."
qu "All of a sudden, Dad stopped shaking. And it all became quiet."
So it is likely that both Lana and Rox died from the same poisoned cocaine. Maybe it also damaged Quinn's mom severely.
Both Quinn and Jill are about the same age (21 or 22), so if Quinn was 7 years old at that time, Jill was likely so, too.
So the whole flashback story of Lana and Rox is ca 14-15 years in the past.
Lana was probably 18, almost 19 years old. If Lana would not have died, she would be around Bella's age (32) today.