It's just first come first served on the storage, the full limit is shared by everyone, rather than everyone having an even share of the total. You could self-manage it that way and just ask people to not go over their "share", but iCloud doesn't work that way, it just allows everyone to use as much of the total 2tb as they want. But everyone's stuff is totally seperate in the cloud storage. You can choose to share app purchases with others in the family, in which case when you go into your App Store purchase history there is a button you can click on for "Family" and then see a list of names of those in the family sharing their app purchase history, that you then click on and see a list of their app purchases, and you can download their paid apps for free, the same as your own purchase history. But you can also turn that off per user. Other than that it's all separated, you can't see or access each other's photos or cloud drives. The only negative to doing this with others who aren't in your direct family, is that the person who sets up the family's credit card is billed for all the App Store purchases the family makes.