Could "What kind of writers ?" be an acceptable translation as well ? The meanings are slightly different though... "What are they like" > "tall, kind, annoying, etc.", whereas "what kind" > "horror, scifi, etc."
"Milyenek az írók" wouldn't be answered by the preferred genre of said writers. If that's what you want to ask, you have to specify it, like: "Milyen műfajban írnak?" (műfaj = genre)
But as has been explained in other places here - in Hungarian, you basically have to use "az" in plural, meaning "writers" (general) and "the writers" (specific) cannot really be distinguished ... therefore both translations should be accepted in English.
... the likelihood of someone asking what writers are like, in general, is pretty low though, but not impossible.
I'm still unclear as to why "How" doesn't fit here. I know I'm not asking about their health if I'm asking how are the writers in English...
In English, we don't usually use "how" to elicit a description of something. We use "what ... like".