A colleague at Means I/O shared this relatable story: "This weekend, my wife said, 'Google says I'm almost out of storage!' I replied, 'We have 2TB with Google One—that's not possible!'" The issue? Setting up Family Sharing on your Google Account doesn't automatically share your Google One storage. You have to enable it manually.
Google One is the premium upgrade to Google Drive, offering expanded storage beyond the free 15GB for Drive, Gmail, and Photos. Share it with up to five family members. Plans start at 100GB for $1.99/month or $19.99/year, scaling to 2TB for $9.99/month or $99.99/year, and up to 30TB for $149.99/month.

If you're on a free account, visit the Google One page to free up space with their helpful tool—though it might tempt you to upgrade.
To share storage, first create a family group:

With your family group set up, enable shared storage:

Family members now access your pooled storage after their 15GB free tier—without granting you access to their files unless shared directly.
To monitor usage, in Google One, select "Storage" on the left, then the dropdown next to "Family storage."