"Can you guys come this weekend?"
My answer "你们这个周末能来吗?" should have been accepted as well - in fact, I'd argue that it's the more acceptable answer in terms of how a native Chinese speaker would actually say it.
This has been the most problematic issue that this course has; the Duolingo team simply considers elongated time positioned first.
Actually, your answer is correct - vice versa.
Yes, native Chinese would be fine with speaking both. Like English, the order of the sentence only depends on what the speaker wants to emphasize (in which the emphasized would be put first)
Not only is also acceptable, but other Duolingo exercises taught me to place the time adverb before the subject. So c'mon! Which one do you want me to use?
Certainly it should be accepted. Nonetheless I don't think it is "more" acceptable and it just depends on the context.