The difference for Marcone and Ivy is that they chose to act with their free will. And as such they are victims to their choices. TWG can't interfere.
How did Marcone and Ivy choose to act with their free will in any way that is meaningfully different than the actions that every person with free will takes?
Also, free will doesn't make it impossible for TWG to interfere, it just makes Him have to be more circumspect. For example, when Michael leaves his kids alone in the house in Grave Peril, he is making the free-willed choice to do so. This does not prevent Father Forthill's car from "coincidentally" breaking down nearby so that there will be someone to watch over Michael's kids.
No, for a couple reasons:
1. The Knight's themselves have attempted to lock the Coin's away from people.
The coins, yes. The coin holders, no. That's the part that I think might be a problem.
2. The Knights don't seek out Coin holders to save them. They show up to stop them, and then attempt to get them to repent before fighting them. If one of them got locked up on Demonreach they got there by their own Choices.
No, the job of the Knights is explicitly to
save the Denarians--stopping them from hurting people is what they do when they
fail to save them.
Also, they picked up the coin by their own choices, so we know that "they made a choice" is not necessarily going to release the Knights from their responsibility to help them.