If you apply logic to it, it's a dumb movie...
How does one return the soul stone? What about Captian America? By the rules set down in the movie, he would never have become an Avenger and would have created a divergent timeline by staying in the 1940s with Peggy. Also wouldn't he have remembered fighting with himself? What was the point of having Captain Marvel? She had...what two...maybe three scenes? Also what if (five years after the events of the previous movie) you moved on...got remarried, had some kids...and now bingo...first wife is back...now what? Let's not even mention that the Hulk is now a wuss and Aunt May didn't get naked. pffttt the movie left a lot to be desired.
You dont understand time travel in this movie. Going back doesnt change the present, and Captain going back doesnt change his past. He goes back and lives his life from that point on beginning in 1945ish in a different timeline with Peggy. Then he returns to his original timeline after to give Sam the shield. Nothing he did before going back changes.
2012 Cap will not remember fighting 2023 Cap because 23 used the scepter containing the mind stone on him at the end to erase that memory.
You return the Soul stone simply by bringing it back to Volmir. What he did whole there is not explained, but they were not the first to retrieve and return the stone.
Thanos is a titan. He is more powerful than his ship. Marvel was able to beat him only because he was unarmored, unarmed, surprised, and dramatically weakened by using the infinity gauntlet twice. He was nearly dead after that.
What happens if your dead wife gets snapped back and you have a new one? I guess everyone has some decisions to make.