Can one family member view what is stored in another family members cloud storage?

See the following from Share iCloud+ with your family - Apple Support

When you share an iCloud+ subscription, everyone in the family group uses their own account. That way your photos, documents, and other information stay private, even though you're sharing access to the service. You simply share the features and space available in iCloud+ with your family members, so you only have one plan to manage.

However you can share select files with anyone as described in Share folders with iCloud Drive - Apple Support

Also, Family Sharing creates a shared photo album; see the following from Family Sharing - Apple

When you set up your family, a shared album is created automatically in the Photos app on all family members’ devices. Everyone can add photos, videos, and comments to the album whenever they like and get notified when something new is added. 

No, unless you share a folder on iCloud with invited people.

With Family Sharing you are sharing the purchases and the storage, but the documents and data you are storing in iCloud are tied to your AppleID.