Not accepting "they are not coming today?" - which is perfectly correct in English in this context.
Wrong nuance. In English, using the normal (non-question) word order in a question is done to express doubt. Dutch works the same way. Your sentence translates the following Dutch question: "Zij komen niet vandaag?"
I don't know, "They don't come today?" doesn't sound like a question to me. I don't hear people phrase questions like that, I've always heard "Do they not come today?" or "Are they not coming today?"
Although in English this would be perfectly fine to say, such as when it's a surprise that they're not coming today. But I would still say it's a wrong translation of this question which sounds more like it's just enquiring if/asking for confirmation of whether they're coming today or not.
They arent coming today? It can be used in a way to sound surprisd and it is also used in enquiring and asking confirmation pn whether they are coming today or not. Im a native english speaker
In English, that word order is somewhere on the border between ungrammatical and very special, expressing a very special emphasis. If it occurred at all, there would likely be quotation marks around "not today".
Therefore: No, it should not be accepted.