Welcome Christmas

This is merely an interpretation from a writer's perspective (a writer who specifically writes children's rhyme and often invents words poetically and understands using unexplained cultural lingo out of the necessity of remaining true to the settings of the otherworldly places he invents)...

fahoo = the words "father" and "Who" smooshed together. Instead of saying "my dad raised me", if you were a Who you might instead (more formally) say "my fahoo raised me".

fores = forest. Commonly disregarded merely as mock-latin meant to sound sing-songy (but otherwise meaningless). l, however, think of this one as how a foreign country's derivative of the French language's "la forét" (or English's "Forrest") might be re-spelled by a culture that has never heard the word used as a name before.

Fahoo Fores = father of the forest. After considering how the song feels so much more like a hymn than a song, I wouldn't doubt that Fahoo Fores is, indeed, a religious moniker meant for guiltless referencing of The [mythological] Lorax (Seuss's titular tree spirit who literally introduces himself by saying that "[he] speak[s] for the trees") with the extreme reverence of not undermining his true name, "Lorax" in vain over usage (the way a song might) accidentally. Although, within a song about "Christmas" sung by Who's with plenty Who-morality, sure, but no directly equivocal "Who-Christ" of their own... my tendency is to compare Seuss's Fahoo Fores to our own universe's idea of our legend of Adam who grew up in a forest (of sorts). And yes, I do mean "The" Adam, of "The" Adam and Eve, from "The" Bible's Book of Genesis.

dahoo = the words "daughter" and "Who" smooshed together. 

dores = gift. This one closely reminds me of the similar sounding Scottish name, Doris, meaning giving one, and Latin's near-match, Deloris, meaning sorrows.

Dahoo Dores = fruit of the forest. This must be another given name of a widely known female Who among Whos (perhaps even a dahoo of The Lorax). Maybe there's a linguistic link to her specific relevance here; the materialistic imagery of Cindy Lou (the youngest dahoo of dahoos) wondering about the disappearance of her family's tree when she catches the grinch stuffing it up the chimney could be a clue. Maybe Dahoo Dores is The Whovian Eve (our bible's original sinner). She could also be either of Adam's daughters (who came after Cain and Abel; Awan or Azura).

ramus = ruler. The German Raginmund that became English's Raymond is a name that means: mighty, protector and counselor.

Fahoo Ramus = first mayor of Whoville. A renowned, trustworthy Who. I guess that he was the first noteworthy mayor of record-worthy Who-lore.

damus = daring one. This one was tough. There's the Greek "Damaris" meaning dominant, the French "Damia" meaning untamed and the Hindi "Dakshayani" meaning competant.

Dahoo Damus = the first mayor's daughter. She was most guessably a brave and noteworthy dahoo of Fahoo Ramus, memorable enough to make it into the final versions of "Welcome Christmas".