Can the caster of an upcast Etherealness spell dismiss it for the other creatures it targets?

Question

When upcast, the etherealness spell lets you target multiple creatures. The spell's description includes the following termination clause (emphasis mine):

You step into the border regions of the Ethereal Plane, in the area where it overlaps with your current plane. You remain in the Border Ethereal for the duration or until you use your action to dismiss the spell. During this time, you can move in any direction. If you move up or down, every foot of movement costs an extra foot. You can see and hear the plane you originated from, but everything there looks gray, and you can't see anything more than 60 feet away.

Prematurely ending the spell seems straightforward for the caster; the caster simply spends their action to dismiss the spell. However, this portion of the spell was written for the spell under its normal casting criteria (i.e. not upcast), which has a typical target of Self.

Compare this to the language used in the astral projection spell, which by default targets other creatures in addition to the caster:

The spell ends for you and your companions when you use your action to dismiss it. When the spell ends, the affected creature returns to its physical body, and it awakens.

and then:

If you are returned to your body prematurely, your companions remain in their astral forms and must find their own way back to their bodies, usually by dropping to 0 hit points.

So in the event that etherealness is upcast and affecting multiple other creatures, does the caster need to spend their action to end the spell for everyone? Or does each character need to spend their action to dismiss the spell on themselves?
Can the other characters even use their actions to end the spell, or could they be trapped on the Ethereal Plane until the spell runs its course?

Answer 1

RAW: The Targets Remain until You Dismiss it

The spell etherealness says clearly:

You remain in the Border Ethereal for the duration or until you use your action to dismiss the spell.

The text is clear. You in spells is always the caster. Like concentration spells like fly, polymorph or invisibility, the releasing of the spell is in the hands of the caster. In the case of concentration, the caster can release freely at any time, but the whole spell at once. This is just that, but without needing to maintain concentration. The text makes it clear you're not dismissing the effects on an individual you are "dismiss[ing] the spell" in whole.

Should the caster be unwilling or unable to dismiss the spell, the spell lasts the duration, as per the text.

It isn't Unreasonable to House Rule

It isn't unreasonable to make a house rule that each creature can dismiss the spell for them as an action; but that isn't what the text says. Even in the case of fly or polymorph or invisibility I've seen DM's handwave control to the party member, unless it was unwilling and there was a savings roll, that the party member can choose to release themselves from the helpful effects. More recent episodes of Critical Role you see Mat Mercer has done just that for at least willing polymorph.

Answer 2

Unclear

I tried to find similar spell (self target, non-concentration, non-instantaneous, upcast targets more creature) but there is none, making this is a unique case and depends on each DM's interpretation.

My interpretation is that the effect of the spell is the spell's description and applies to each target affected,

... until you use your action to dismiss the spell.

'you' in this sentence refer to the creature affected, hence they can end the spell on themselves with an action. The caster can only end the spell affecting themselves, not the other creature, because etherealness is not a concentration spell.

But it's a single spell affecting multiple targets, thus using an action to dismiss the spell ends the spell for everyone?

I'm using the ruling from Sage Advice Compendium as precedent:

If dispel magic targets the magical effect from bless cast by a cleric, does it remove the effect on all the targets? Dispel magic ends a spell on one target. It doesn’t end the same spell on other targets.

The bless is one casting of spell, but dispel magic only ends the spell on the target, thus setting a precedent that 'ending a spell on one target' does not necessarily end the spell on the other targets, regardless the fact that it is caused by single casting of spell.
So, each of target affected by etherealness may only end the spell on themselves.