This might be the best way to go about it. Wireguard has an iOS client and it should be easy to set up. I’ve done this for dumber devices, should be okay.
Or frankly, some others here are mentioning that logging in to one service doesn’t automatically log you into all of them. So maybe I’d be giving my family member more flexibility by not limiting them to a small number of servers as defined in the configs, since each one needs a file and picking among them is annoying if there’s an issue.
That said, going from 5 euro a month for Mullvad to 5 + 10 to add Proton does add up, and to be honest, a second free Proton address and a second Mullvad subscription (and investing in a more local solution instead of getting tied down to Proton Drive) might be better for me.
But I haven’t made any decisions just yet. The 500GB of storage might just end up swaying me.