Endgame plot has holes in it

Rating: 8/10 (11 October 2019)

Lowered rating from 8 to 7 after rewatching the movie. The plot kind of folds on itself at the end. Iron Man/Tony Stark wipes out 2014 Thanos.
Now this gets a bit confusing. Infinity War happens during 2018 giving Avengers the reason to do what they do in Endgame. During this timeline Thanos lives until Thor goes for the head after Thanos destroyed the stones forcing the Avengers to time travel. All goes fine until future Nebula gets caught by 2014 Thanos who then "dies" in the future. In other words Thanos dies on the timeline where Infinity war happened before infinity war happened but didn't happen because he disappeared in 2014. But how? Nothing should have happened when Iron Man snapped his fingers. Why? Because snapping 2014 Thanos out of existence makes snapping 2014 Thanos out of existence impossible.
This the third snap was impossible to happen. And I mean really impossible. Not the fake impossible that scientists use to discribe things they don't understand.