This is an area that Monzo’s apparently got a lot of ideas about.
Here’s Tom’s comment on Monzo providing accounts for under 18 year olds -
https://community.monzo.com/t/monzo-card-for-under-18s/1689/6?u=alexs
bearing in mind that Monzo’s expecting to be ready to start providing current accounts by the end of Q1.
My guess is that the shared pots functionality that Hugo mentioned here & here which is probably this card on the roadmap, might provide the functionality that you’ve described or could at least be adapted to provide it. You can already do P2P transfers between Monzo users so if the family member had their own card, funding it wouldn’t be a problem.
Just to give you a slightly better sense of what to expect, Monzo’s not planning to offer ‘conventional’ joint accounts. And based on the discussions that I’ve seen, it sounds like Monzo want to come up with a digital solution (for want of a better phrase) in the app, as opposed to creating a dedicated type of bank account for this sort of thing.
My guess is that everyone will have their own cards with their own funds, then join a group which has a shared balance that everyone can deduct payments from. Members of the group might even be able to see the details of each other’s transactions & / or a spend by category summary - or it would be great if they could anyway 
in fact, if you imagine the Targets page
but with family members names (or different bills for the pot shared by students) instead of category names, that might be what Hugo was hinting at, when he said that -
& if you look at the design of Targets, from the API it looks like there is some flexibility built in, to enable them to be used with other things, besides categories (although this could just be future proofing of course)
