I know for college kids Juul is the rage right now.
What about the Blu pod? It's cute looking and small and, although not billed as refillable, it is easy to refill. (used to be My Von earl but Blu purchased them). It charges in about 20 minutes.
You could get them each a blu unit (they are having an introductory offer for $1)
Set a goal of refilling each pod once ---2 pods run about 8.99.
Then find a
juice they like - buy a big bottle of it and give them each a small plastic bottle with extra juice.
I use different equipment but carry the blu as an extra and I refilled the pod twice with no problem at all.