If you bring up the timeline, you will see there are specific scenes for each individual in the timeline when you highlight them. To satisfy the requirements for this trophy, you don't have to fill the timeline to 100% for each individual (as some become empty or pointless after a while) but instead have the scenes seen.
For Chapter Three, there are:
Four scenes to watch for Gustav
Four scenes to watch for Flora
Four scenes to watch for Swan
Two scenes to watch for Vandenberg
Four scenes to watch for Edison
Four scenes to watch for Bernhardt
Four scenes to watch for Mundy
No scenes to watch for Tesla
Confirm what scenes you have seen by, like I said, going into the timeline readout for each individual and making sure that all of these are showing. I would suggest leaving some for later (working your way left to right) as some reveal more information that doesn't necessarily make sense until you've seen other scenes. Whether or not you ride out someone to the end of Chapter Four before moving on to another is entirely up to you, too.