Hey no problem. I've noticed some inconsistency with using trains to test these mods. For example, after first installing Animals AIO the trains seemed to not be spawning. I felt unsure about this so I went to St Denis and there were people on the trams. I then slept in-game until the next morning and trains were spawning fine again and with passengers.
I also came across a situation today in which a train seemed to go past my position without spawning (I'm using Railway Engineer to view their icons on the map and radar) and then when it was further past me its icon indicated that it spawned, so I caught up to it and it was indeed driving along the tracks and with passengers.
Later on I'll try to view them from a distance more to see if they have peds without being up close to them as you mention. At this point though, if trains are generally working, wildlife is good and people are on trams etc. then I'm considering it working enough to use the mods. I'll take an occasional oddity with a train over not using the mods given the visual improvement they provide, though I'll still be avoiding any that consistently reduce/break spawns.
You're right about this all being confusing and it's difficult to find consistent findings - especially with different people having different experiences based on their systems/settings etc. I do think dominatorgt is onto something though. He seems to have solved these issues for his own game, and the conversations he's started on nexus have been the best public resources I've come across so far for shedding some light on this from a technical standpoint. His posts can be difficult to understand as they're quite technical and he's using a language translator, but it feels like it's being pieced together and I think this will continue to develop. It seems to be a bit of a work in progress, but at least it's being actively looked at by multiple people with more coding knowledge. One interesting point is that he apparently uses one custom install file for all/a lot of his mods. His terrain instructions that I mentioned before also included using one install file for multiple mods so I'll be interested to learn more about that and how to put it together correctly.
Anyway, the situation certainly feels more hopeful now than it did previously and I'm looking forward to learning more!