The Underworld and Earth
- Casper: Nephew to Stretch, Stinkie and Fatso.
- Stretch: Sibling to Stinkie and Fatso - Uncle to Casper.
- Stinkie: Sibling to Stretch and Fatso - Uncle to Casper.
- Fatso: Sibling to Stretch and Stinkie - Uncle to Casper.
- Grandma Smoochy: Aunt to Stretch, Stinkie and Fatso - Grandmother to Casper.
- Spitzy: Aunt to Stretch, Stinkie and Fatso - Great-aunt to Casper.
- Jasper: Great uncle to Casper.
- Most of the family has blue eyes.
- In "Ghost Magnet" Grandma Smoochy calls Casper's uncles her nephews, which could mean that if she is the grandmother of Casper, the Ghostly Trio are actually his first cousins once removed.