Yes but billions of years in the future, and just because the kids have conditional immortality doesn’t mean the planet does.

Harley knew, he had the frog ruins that the game code comes from and owns the company the distributed it. Mom Lalonde worked for Skaianet so she knew. Dad probably had a vague idea based off the text Nannasprite wrote in 
Colonel Sassacre’s Daunting Text that got sent back with John as a baby.

Bro on the other hand, I’m not sure. maybe he’s just that cool, maybe Lil Cal told him about it  ¯\_(ツ)_/¯

Nothing out right, but there are some examples earlier on like Jade and Jadesprite interaction, or Dirk comparing himself to Bro. Here’s a really good analysis/theory on ultimate selves if you’re interested. 

No prob bob. It happens all the time

Those are the Beta kids. Beta kids had a few doomed timelines

It wasn’t stated, they didn’t have someone that could time travel to create any until Game Over

As long as their dreamself isn’t their mainself they can change it as much as they like. (See Jade growing and ungrowing multiple limbs)

The only doomed timeline they had was Game Over

“Metamorphosis is clearly a significant part of troll biology, and therefore ingrained in their mythology. They’ve got cocoons everywhere, and are often likened to insects through biological terms. The wings have nothing (we know of) to do with troll adulthood. But have a lot to do with their perception of what ascension should be, which is the culmination of a pupation process. Which is why some may look to fairies as an ideal, or rule them out as fiction on account of the ideal they represent. Ascended trolls in this game are essentially magical fairies.

Humans do not have a good analog for this though, and enjoy no biological upgrades. Only powers and fashion.”