iCloud Photos are private unless you intentionally share them via How to use iCloud Shared Photo Library - Apple Support
or via How to use Shared Albums in Photos on your iPhone, iPad, and Mac - Apple Support
Even if you share an iCloud Storage plan with your family, the photos are still private unless you share them. 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.