These are common last names for Hobbit families in Bree; many of them are also common in the Shire (for the obvious reason that most of them refer to places where Hobbits might live).
Bill Ferny is a Bree-lander with "an evil name" (1.10.24) in the area – he is the "swarthy Bree-lander" (1.9.67) talking to the "squinty-eyed southerner" (1.9.67) in The Prancing Pony common room when Frodo slips the Ring on by accident and disappears. Frodo notices that Bill Ferny leaves quickly after his sudden disappearance, and Strider fears that Ferny will bring news of Frodo's Ring-related activities to the Black Riders searching for him in Bree. And in fact, this turns out to be true: on his walk that night, Merry overhears Ferny muttering something to a hissing voice, and Aragorn is sure that Ferny has told all of the news of "Mr. Underhill" to a Black Rider.
As Frodo, Aragorn, Sam, Merry, and Pippin walk out of Bree with Bill the Pony, they walk past Bill Ferny's dark, ill-kept house. Ferny is leaning over the fence, and he shouts a few nasty things after our heroes. In response, Sam warns him to "put [his] ugly face out of sight, or it will get hurt" (1.11.42). Then he throws an apple at Ferny's nose, causing him to howl with pain. Aragorn is sure that Ferny will pass on the news of the party's direction to their enemies.
Bob keeps the stables at The Prancing Pony inn at Bree. He's the one who finds the Hobbits a pony to buy after all their steeds have bolted, following the attack on the inn by the Black Riders. After Frodo's party leaves The Prancing Pony, when Tom Bombadil sends their lost ponies to Butterbur, Bob works them hard but treats them well.
Harry is the Bree gatekeeper. When Frodo, Sam, Pippin, and Merry arrive in Bree, he asks them probing questions about their business that Frodo can't (and won't) answer. Merry reminds Harry that Bree is supposed to be friendly to strangers, but Harry points out that there are weird folk about. And when Frodo accidentally slips on his Ring right in the middle of The Prancing Pony, Harry slips out of the inn, which frightens Frodo – who might he be reporting to? Aragorn wonders if Harry is in the power of the Black Riders: "[Bill Ferny] had words with Harry at West-gate on Monday. I was watching them. He was white and shaking when they left him" (1.10.111).
Mr. Mugwort is the Bree Hobbit who complains to Butterbur that he saw "Mr. Underhill" (a.k.a. Frodo) disappear into thin air after singing his song. Frodo appears and assures Mr. Mugwort that, "Of course there's a mistake [...] I haven't vanished. Here I am! I've just been having a few words with Strider in the corner" (1.9.84).
Nob the Hobbit works for Barliman Butterbur at The Prancing Pony. He’s generally a cheerful and friendly guy. We first catch a glimpse of Nob when Butterbur sends him off with a message to Bob the stable boy to find room for the Hobbits' five ponies. Nob also comes to offer the Hobbits drink, and he brings them their meal after they have washed. Later, when Butterbur tells Frodo of the Black Riders visiting, he mentions that Nob saw them as well, and that his "hair was all stood on end" (1.10.51). When Merry doesn't come back from his evening stroll, Butterbur sends Nob out with a lantern. Nob finds Merry unconscious near Bill Ferny's house. And when the Black Riders are searching Bree for the four Hobbits, it's Nob who ruffles their beds, puts pillows under their blankets, and even makes "an imitation of your head with a brown woolen mat, Mr. Bag – Underhill, sir" (1.10.115). So Nob is a useful Hobbit to have around – like Dobby the house-elf, but in Hobbit form.
These are common last names for human families in Bree.
This nameless character is an ugly companion of Bill Ferny's. When the Hobbits first come to The Prancing Pony, he is in the common-room loudly proclaiming that the North (i.e., Bree-land and its general area) is soon going to have a huge number of refugees from the South thanks to rising troubles and violence. He is there at the inn when Frodo does his little disappearing trick, and he leaves The Prancing Pony in Bill Ferny's company right after this event. He is also the one guest at the inn who disappears without a trace after the horses bolt in the night from Butterbur's stables. Suspicion immediately falls on him as a horse-thief, since only one of the horses is actually missing. Butterbur wants his companions to account for his whereabouts, but "it appeared that he was nobody's friend, and nobody could recollect when he had joined their party" (1.11.31). Suspicious...
As the Hobbits leave Bree, Frodo sees a dark house at the outskirts of the village – Bill Ferny's house. Frodo catches sight of "a sallow face with sly, slanting eyes" (1.11.36). He realizes that that's where the Southerner is hiding. Frodo also thinks, notably, that, "he looks more than half like a goblin" (1.11.37). Throughout the rest of the series, there are strong hints that this man must, in fact, be part Orc.
The men who come from Isengard provoke the Ent Treebeard to think, "Are they Men he has ruined, or has he blended the races of Orcs and Men? That would be a black evil!" (The Two Towers 3.4.89). Once the returning Hobbits see the squint-eyed Southerners who are harassing the Shire at the end of the The Return of the King, Sam observes, "Like that friend of Bill Ferny's at Bree," to which Merry answers, "Like many that I saw at Isengard" (6.8.78-9). So these cruel Southerners aren't just mean guys; they are also a race of part-Orcs. The squint-eyed Southerner's presence in Bree this early in the series foreshadows the danger even to the Shire from the plans of Saruman and Sauron.