My initial reply is to say both Henry & Emma would probably be apparitions ( visions ) of consequences/actions taken while everyone is inside this / under the influence of this veil.
( a media example would be ‘Inception’. The scene where Fischer follows the blonde in the red dress . He perceives a woman – when in reality – it’s Cobb. ) Something like that – whereby Emma & Henry would be the desires/wants of Charming/Snow. Then, since everyone in this ‘reality’ is interconnected, they too would share in their wants/dream(s) – which would lead to physical manifestation of the want.
Or – put more simply.
That’s a good question & I don’t quite know.
: D