Translation:Two writers are writing next to the table.
Én is szeretném tudni miért nem írjuk: "két író ír az asztalon" vagy "az asztalnál"
"Asztalon írni" sounds simply illogical. "Asztalnál" is what most people say i think but the traditional way of expressing this is somehow "mellett". It may also sound illogical but then explain me "to cut down trees"!
"Two writers are writing at the table" is accepted now. I suppose "at the table" should be reported wherever "az asztal mellett" turns up.
Only their length. It's only that when you say "one plus two" it's never "egy meg két" but "egy meg kettő". And also: if you say "(i want) both" , it's "mind(a)kettőt kérem", there's no such form as mindkétet or mindkétből (ablative) etc. But in attributive (?) function it can be "mind(a)két (ház/-at/-ból)" And when you say "mind(a)ketten" it's "both of us/you (pl.)/them", but only if it's the subject of the sentence. (We/You/They both hate this= Mindketten utál-juk/játok/ják ezt) If not it's "mind(a)/kettőnk-suffix/kettőtök-suffix/kettőjük-suffix". So there is no forms like "mind(a)két-ünk/-etek/-jük" either. Nor "két/-et/-ből". "Két" only appers when it's a number-attribute (for example "két összeillő ember"= two matching people) or when counting (egy, két, há'...) so there is no "két van" for "it's two (o'clock)" but only "kettő van". Neither "kétem van" only "kettőm van" meaning "I have two". In any other case they can undisturbedly be used alternately. And of course Hungarians tend to say "két" in the spirit of economy. It's just less time. One more thing: There are two of them = Ketten vannak.
"Next to the table" to me means that those two poor writers are hunched back sitting on the floor next to a lonely table. The correct way of expressing that you write sitting "at the table" -- forget "next to"