How do I share my iCloud storage to family members on my plan?

Hello,

This Apple Support article has information about sharing an iCloud+ subscription.

Share iCloud+ with your family - Apple Support

”Share iCloud+ with everyone in your family

To share iCloud+, you need iOS 11 or later, iPadOS, or macOS 10.13 High Sierra or later. For the best experience, make sure your family members' devices meet these requirements, too.

On your iPhone, iPad, or iPod touch

1. If you haven't set up Family Sharing yet, set up Family Sharing. 
2. Go to Settings > [your name].
3. Tap Family Sharing.
4. Tap iCloud Storage.
5. Follow the steps to share your existing plan.
6. Use Messages to let any family members with an existing iCloud+ plan know that they can now switch to your shared iCloud+ plan.“

I hope this helps.

See this.

Share iCloud+ with your family - Apple Support