Pippin is the son of the Thrain, who is the hobbits’ stand-in for the absent King in Gondor.

Frodo is a Baggins, but like Bilbo has Took relations, as both families are old, powerful, and often intermarried. His family also owns much of the land in and around Hobbiton. So basically landed gentry in all but name.

Merry is the son of the Master of Buckland, one of the oldest families running one of the oldest parts of the Shire. So also basically landed gentry.

Gimli is a descendant of Durin, although not in a direct oldest-son line like Thorin was.

And of course Boromir is the son of the Steward, who was just shy of a king in all but name.