If I share my cloud can they see what’s in my storage

No. iCloud+ sharing does not give other's access to your files nor you access to theirs. It merely shares the storage space, but data and files remain entirely separate and private.

See the following link for more details. click here ➜ 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.