5. Why has Logan kept Henry alive?

So Logan is from HFM, Henry is the Fae that helped Seth, and Logan keeps him alive to torture him.

6. How did Chelsea interrogate the people at Logan's prison without the
Elders sensing her power?

Logan and Gabriel both know Kaden and Etta. Chelsea was the one that didn't know Etta. Etta on the other hand had seen with her gift that she'd be helping Chelsea. When Chelsea is interrogating people at Logan's prison, they do it there because Etta has spelled the prison. When someone is in Logan's prison... just think of it as they're showing a dead signal even though they're alive. This question is sort of answered by two different stories.

You learn in HFM that Etta spelled the prison for Logan, but then in Unbroken/Undivided the prison is mentioned.

7. What's so important about the identical marks/scars, on the R-43 people?
Was it from implants? Like a control chip? Something to block memories? Tracking device? Or experiments that worked, but were more than a serum or what was in the gas?

Okay so the R-43 people. You learn different things in snippets here as well but the most important pieces come from Kieran talking about missing time. I don't know if people remember, he says that he would be in a room, the mist would come – or they would inject him with something. He wouldn't remember a single thing, but, he would note that time, more than he thought had gone by.

The next bit of information comes from Kaden and Keiran's story. Kieran has an ability, two of them. He can change who he is, and hide his scent, but it's not hiding exactly because Oakley can smell him. Chelsea cannot. Kaden, he also has the ability but it's different. Tweaked. He lost his wolf, BUT he can transform into Reese.

R43 is the tattoo they gave the people that were able to be success stories [but outside of their capture/torture and abilities you don't exactly know what they are REALLY successful of].