Some guesses and theories...

The only thing you need to know is that all of the superheroes will be alive and well by the end of the film.
Look at the marvel comics history - they've all died and came back from the dead like a hundred times.

Interesting theories. Like a number of probable theories out there, we’re gonna have to wait and see if any of them prove to be right on the money (I gotta stop reading any more in case any come true and spoil the surprise lol). That said, getting a recap/scene of Clint witnessing his family disintegrating feels like a guarantee.

Now one popular theory that I personally think sorta has merit, is the Skrull theory. As Skrulls are going to be making their grand debut in Captain Marvel, it’s been theorized that some familiar faces in the MCU, be it heroes or villains, will ultimately be revealed as Skrulls in Endgame. This should be expected in Captain Marvel, but how about Endgame? They’ll probably be dealt with in CM but I doubt that will be the last we see of them. If they have anything to do with Endgame though, I guess we’ll find out sooner rather than later...

I think Captain Marvel's role will be to use the Infinity Gauntlet (or the newly created gauntlet is those rumors are true) to "unsnap" everything. Her ability to channel and manipulate energy seems like the best bet to handle the power of the Infinity Stones.

Also, I have a sneaking suspicion that Steve and Tony will survive the movie one way or another. It seems like too much of a foregone conclusion that they die. Instead, they'll either retire, be brought to a different timeline, or maybe go off into space to ensure no one else will ever use the Infinity Stones or something.

Interesting theories, but some are maybe a bit too deus ex machina? Marvel tends not to rely on that sort of thing to wrap up stories, and doing so might make the audience feel cheated.

I do think there's merit to some of your ideas, especially about heroes being tied into the stones. We know that Vision, as Jarvis, was able to exert his will against Ultron even when he was in fragmented form, so the idea that Vision imparted some or all of his psyche into the Mind Stone before Thanos took it makes sense. He likely knew that Thanos could use the Time Stone to undo anything Wanda did, and that was a charade, albeit a powerfully sad one, he underwent in order to deceive Thanos. He may have shunted the seemingly extinguished lives into some other reality where they can be rescued via the Quantum Realm.

I also like the idea of heroes wielding Infinity Stones. I could even see it happening as an aftermath of the battle, where each hero can use a stone to make some change. Six original Avengers, six infinity stones. Hulk might well use the Mind Stone to merge he and Banner, allowing both to share both bodies, Captain America might realize use the Time Stone to return to 1945 and live out his life with Peggy Carter (or bring her into the present?), Thor could use the Soul Stone to resurrect Asgard's fallen people (hello Heimdall and Loki!), etc. Maybe Hawkeye will use the Power Stone to finally be able to stand toe-to-toe with his crew, LOL.