can family member see their kids iCloud Photos?

Hello daamna,

When in a Family Share, no data is shared unless the owner of the Apple ID explicitly says they want it to be shared.

Purchase Sharing can be enabled for sharing purchases and subscriptions - How to share purchases with your family - Apple Support.

If you want to share iCloud Photos, you'll need to turn on Shared Library. You can also setup Shared Albums to achieve this as well.

1. How to use iCloud Shared Photo Library - Apple Support
2. Use iCloud Shared Photo Library on iPhone - Apple Support

By default, you will not be able to see their photos and they will not be able to see yours.

Only if they are added to a shared album.

click here ➜ How to use Shared Albums in Photos on your iPhone, iPad, and Mac - Apple Support