What is the name of Bilbo Baggins' thievish relatives?

Bilbo Baggins’s thievish relatives are the Sackville-Bagginses.

The Sackville-Bagginses are Bilbo’s acquisitive, socially ambitious cousins in J. R. R. Tolkien’s Middle-earth. The family includes Otho Sackville-Baggins, his wife Lobelia, and their son Lotho. They are portrayed as grasping and status-conscious, contrasting with Bilbo’s comfortable but adventurous nature.

When Bilbo leaves Bag End for his journey to Erebor, the Sackville-Bagginses assume he has died and try to benefit from the situation. They begin arranging an auction of his belongings and hope to acquire his home. Bilbo’s return frustrates their plans, while his decision to name Frodo his heir makes them even more resentful.

Their “thievish” reputation comes from their attempted appropriation of Bilbo’s property rather than from professional burglary. Bilbo himself becomes the actual burglar of the story, hired by Thorin Oakenshield to enter Smaug’s lair. The Boffins, Brandybucks, and Tooks are other Hobbit families, but none is Bilbo’s grasping branch of relatives.