Avengers: Endgame (2019)
Incorrectly regarded as goofs
It is reasonable to presume the Pegasus are raised in one of the other Realms, or are constructs of the will power of the Valkyrie.
Strange is established as having seen the future and is attempting to ensure that they'll have the one future (out of over 14 million possible futures) where they win. The characters who were not there were not summoned, because Strange had not seen them there. They might have been there in some of the possible futures, where the heroes lost. Which would give Strange a motivation to not summon them.
Incorrectly regarded as goofs
But for almost every stone, it's going to be difficult, if not impossible, to return it without anyone seeing the difference - some stones were stored in containers that were broken, others were in artifacts that were destroyed to get to the stones.
Further, when Steve Rogers goes to return them, we very specifically see him with ONLY the stones, and not their original artifacts, or any way to repair the containers.
Apparently Steve must only deliver the stones to the moment they were taken from the past. Because as the Ancient One explained, the stones create the flow of time and removing one of the stones causes that flow to split. So Cap didn't have to (let's say) put the Aether back into Jane. As long as the Aether (reality stone) exists in that timeline, that's enough for the timeline not to split.
It was never actually stated that 5 hours of quantum time is directly proportional to 5 years of real time. In that same scene from Ant-Man and the Wasp, Janet warns Scott to not get sucked up into a time vortex, which makes it obvious that he did accidentally travel through a time vortex and ended up five years in the future. Scott was very well aware of this, which is why he proposed to the Avengers to find a means of controlling the time vortex so that they could use time travel to reverse Thanos' actions from Infinity War.
The population is more than doubled, since some births would have occurred in the intervening 5 years. They'd live at the same places, that they had five years ago. When Scott Lang makes it out of the quantum realm, he walks past rows of empty houses.
As for food, when the snap is undone, Scott sees birds suddenly appearing, suggesting that the snap extended to animals as well, which would now have doubled (supplying people with more to eat). fields on farms could be replanted, since with fewer people to feed, the fields would've been left to fallow. In Infinity War, Thanos notes that Gamora's planet had a surplus of food and resources, after he wiped out half of the population. Applying it to Earth, the world would've had a surplus of food, for the last five years. At worst, society would have to institute ration cards (as many countries did during the world wars), until more food can be produced.
When 2014 Thanos arrives in the present day (thanks to 2014 Nebula) this would create a time paradox - as Thanos no longer exists in the past the events of Avengers: Infinity War would not come to pass. Thanos would not be around to collect the Infinity Stones and the Snap would not happen. Akin to the 'Grandfather Paradox' The other explanation for this is the events of Endgame create a slightly alternate timeline, whereby the events of the MCU remain unchanged and cannon while a new alternative timeline has been created in another reality whereby Thanos disappears from events in 2014 and the Infinity War storyline does not take place - similar to the conversation between Bruce Banner and The Ancient One. Another possible explanation is that, when the stones needed to be returned, Steve Rogers had to return them to almost the exact moments from whence they were stolen, which means that he would have returned the Power Stone to the moment in 2014 when Thanos and Nebula still existed.
In previous films (more particularly Guardians of the Galaxy), it is established that only direct bodily contact with an infinity stone will cause that person to be destroyed, unless that person is a species that could withstand it (such as a Kree, Celestial, Titan, etc.). It's also established that any kind of weapon or gauntlet would allow the wielder to use the power of the stone(s). This being the case, Tony attaching the stones to his Iron Man gauntlet would have allowed him to use the stones (although still having a huge amount of energy flowing through him), but it is perfectly accurate that the energy was enough to kill him when he snapped his fingers.
First as stated by the Ancient One the Infinity Stones are essential to the flow of time and since Vision has only ever existed with Mind Stone in his head cannot be brought to the current time line as the stones had to be brought back to their original places.An while bringing Black Widow and Tony from the past could work it would defeat the whole purpose of their sacrifice to save the universe. Also it has to be taken into Account that Doctor Strange already saw all potential time lines and the only way for them to win was for Tony to make the ultimate sacrifice - if Tony lived then the outcome would not happen.