OK, this is a small but confusing thing. With iCloud, you get a base of 5GB of free storage for each family member. Needless to say this doesn’t last long, with a few two-minute videos, you are going to be a 4GB. So, if you buy the $0.99/month plan you get 50GB, the problem is that by default family sharing is not turned on, so if you just buy it on your machine, your family is in bad shape.
The solution is to go to Settings > iCloud > Subscriptions and turn on Family Sharing for subscriptions are you are good to go.
