Can everyone sharing the plan use their own iCloud ID?

"With Family Sharing, you can share a subscription to iCloud+ with everyone in your family group. This includes 50GB, 200GB, or 2TB of iCloud storage as well as features like iCloud Private Relay, Hide My Email, and HomeKit Secure Video support" Click on this link to learn how to 'Share an iCloud storage plan with your family' --> https://support.apple.com/HT208147

Yes, you each use your own ID. The entire storage upgrade level is shared by all users in common but each user's data remain private. Each person can take as much or as little storage as they wish until it is all taken by the entire family.

Yes. Everyone should have their own Apple ID.