I’m 99.9% sure this has been discussed but couldn’t find anything in a search but would it be possible to have an Account that you can authorise the use of Multiple cards, a bit like the way Apple handle Family iTunes/iCloud accounts.
E.g. We have the main account as it is but in the App you link a card for other family members and set a limit to what they can use.
Like your child going on a school trip, you can authorise that card to access £20 of your account balance.
So those cards don’t actually hold any money but are used as a gateway to your main account.
Not sure if I explained that very well? lol