Joe Russo did a q&a in China
https://www.reddit.com/r/marvelstudi...ngers_endgame/
Q: Can you get the soul your sacrificed for the Soul Stone back when you return it?
A: No, the process is irreversible. Even if you have returned it to its original location, you wouldn't be able to get the person back. In fact, it's not really returning the stone, more like put it back properly. The tribute soul for the soul stone will forever be sealed in that place, therefore Black Widow is gone forever.
Q: How did Thanos bring his army to the future?
A: There is a guy called Maw in his army, he was a great wizard. Thanos himself was a brilliant genius as well. Those two easily reverse engineered and mass produced Pym Particles.
Q: What about those people who got dusted? What did those five years mean to them? Why didn't they grow older when undusted?
A: Yes, those people whom was lucky to survive the snap are 5 years older than the people who just got back. The reason Spider Man saw his friend again in high school at the end was simply because his friends was unfortunately also dusted like Spider Man was. Of course, there are people in his grade whom didn't die and they are probably already in colleges by now. To those dusted people, they had no conscious in these past 5 years. They didn't know what happened. It's as if they had just woke up from a long sleep. The only one who was aware about how many years has passed was Doctor Strange, because he has already seen that when he was time mediating on Titan. Parker's reunion with Ned was a touching moment. There are also people whom indeed moved on but suddenly was reunited with their lost ones. Yeah it's kind a complicated world now.
Q: EG's plot, is it a parallel universe or a closed time loop?
A: Nope, not a time loop. Both Ancient One and Hulk were right. You can't change the future by simply going back to past. But it's possible to create a different alternate future. It's not butterfly effect. Every decision you made in the past could potentially create a new timeline. For example, the old Cap at the end movie, he lived his married life in a different universe from the main one. He had to make another jump back to the main universe at the end to give the shield to Sam.