I have UK employees overseas paid in EUR to non named mastercards which I provide them.
If thier wives have monzo… Does the app allow debit top up, from a card that isnt the owners name ??
I will assume the EUR -> GBP conversion is going to happen at the other card provider at mastercard rates ??
I did the initial top off on my wife’s card and it worked fine. I tested it again once it was fully active and again, topped up no problem, but…
The card details are stored on her phone, she can top up whenever she wants! The only way to remove these details is to add a different card.
Yes it would solve a logistical hurdle that some of my guys face though… They end up using transferwise to send thier wives funds.
Any ‘over charging’ by the wife is down to them to solve not me 
Yes, it is possible to top-up using a debit card with a name different to the account holder 
The only thing to be wary of is that top ups are always in GBP. That means if they’re topping up using a non-UK debit card the bank may charge you a fee for the conversion.