If number 2 happens, where might Edward and his brother get support from? Former ricardians, or?
Former Yorkists more generally. Maybe the Woodville clique and Dorset (depending on if they want to stir things up or not),
Also in the second scenario, would Henry know they were still alive, would everyone? If so does this butterfly Henry's support, force him to fight for them? Or would he even repeal the act that made them bastards?
If they only come out of the Tower in the chaos after Bosworth and then flee abroad (to Burgundy most likely) Henry either...
1) Genuinely believes that they are impostors and proclaims them as such. In which case it comes down to whether they can do a better job convincing people they are genuine than Warbeck and, importantly, pick up more domestic supporters in England.
2) Knows they are genuine and still tries to claim they are impostors. In which case same as above. Some more optimistic/romantically-minded people claim this is what happened with Perkin IOTL.
3) Knows they are genuine and therefor doesn't repeal
Titulus Regius and probably doesn't marry Elizabeth (with two living brothers she doesn't bolster his claim much, and could potentially destabilise his regime from the inside). In which case Henry will be relying on his own very weak claim to throne and one of his justifications for deposing Richard ("shedding of infants' blood") is demonstrably false.
In such a scenario where they emerge from the Tower they might join up with Elizabeth Woodville and their sisters, and if they (and other retainers) publicly and openly acknowledge the two boys to be genuine then a hell of a lot of people are going to believe them and they can probably counterattack England and retake it from Henry (if indeed Henry even manages to secure control of the country).
Of course having them survive like that has other butterflies- maybe the rumours about their demise don't grow as virulent if they're actually alive, maybe as a result of this their Woodville uncles and Grey half-brother don't defect, maybe other Edwardian loyalists don't defect, maybe the Buckingham rebellion turns out radically different, maybe the Stanleys are less troublesome (William got executed IOTL for saying he wouldn't fight Perkin if he knew he was Edward's son), Richard can whip them out of the Tower and say "nuh-uh, I didn't kill my nephews". So all-in-all, there's no guarantee Bosworth will go the way it did or even happen in any recognisable form.