I would like to increase the iCloud storage for a family member - how can I do that?

Hello,

I am assuming you do not have Family Sharing going, or at least you do not have a Family Sharing level subscription or simply have not set up to share purchases.

I have not heard of gifting storage so you probably either have to gift them the funds so they can subscribe to more, or you need to subscribe to a Family Sharing level plan and invite them to Family Sharing.

Share an iCloud storage plan with your family - Apple Support - "With Family Sharing, your family can share a single 200GB or 2TB storage plan" https://support.apple.com/HT208147

iCloud family sharing can only be done if you have at least 200 GB iCloud Storage subscription.