I have not read the whole thread, so forgive me if this has been talked about here already. Also, I have only seen the movie once so far so I might have missed something, but here is my take on the time travel stuff:
I think there is only one timeline.
Ancient one said that the stones actually created the flow of time, and if one was removed it would branch into a new timeline that was unprotected. But then Bruce said that by returning the stones it would heal the timeline and bring it back into alignment. I took this to mean that the stones themselves would bring the timelines back together, not so much that returning them would undo the fact that they took them.
If I'm right then the power of the stones would make it so that whatever you did in the past was what was always done.
I'm not sure how the fact that Loki escapes or Thanos jumping forward and gets dusted gels with this, but these are reality warping magic space rocks ¯\_(ツ)_/¯
Maybe the new Loki show will end with his recapture, thus restoring that timeline. The "Hail Hydra" moment could be attributed to Loki, so Sitwell and company don't think cap knows. And past Cap got hit by the scepter so probably just forgot what future Cap said about Bucky.
The 2014 jump is harder to hand-wave away and my only idea on how that would line back up would be if when Tony dusted him and his army he reset them back in 2014 instead of just erasing them. That doesn't seem like something Tony would do, but maybe the stones did in spite of him? The stones are supposed to be somewhat sentient, especially the mind and soul stones, after all.
Maybe the stones are working outside of time, so when Thanos' snapped and dusted half the population, and Hulk snapped them back, that was more or less simultaneous. Like the snaps worked together to move that half from 2018 to 2023. Seems a bit of a stretch, but who knows.
EDIT: punctuation