I think your distinctions between some and any sound correct, though I can't guarantee for certain that there are no exceptions.
Someone and anyone do not have a set rule, however. There isn't a hard-and-fast rule; they're used differently in different situations. In some situations there is a slight difference between them, in others I would consider them nearly interchangeable, and in others you must choose one or the other to be properly understood as they can have entirely disparate meanings.
John Lawler's answer here on ELU attempts to explain why there is no set rule for when to use someone and anyone:
You are correct. There is no clear way to do this. Robin Lakoff's paper entitled "Some Reasons Why There Can't Be some ~ any Rule" is precisely about this situation.
Short summary of a few of the reasons:
- Any is a Negative Polarity Item, but some isn't.
- Many environments (like questions) allow NPIs like any, but don't disallow some.
- There are several kinds of any, including NPI any, and "Free Choice" any, as in
- Any idiot can solve this problem.
And to answer the question in your title, it's idiomatic to use anyone there; "Is there anyone among you who knows the answer?" (that is, more than one of them could know it). So it should read:
Does anyone know the answer?
Whether is not a question word, although it looks like one.
Question words beginning with wh are the following:
- what
- which
- where
- who
- whose
- when
- why
The rule for making questions using question words is fairly simple:
Question word + auxiliary + subject + infinite or, "QUASI" is a useful acronym. (It is not infallible but it works most of the time)
1) Which colour did she choose to make it? Blue or green? (if there is a limited choice)
2) What colours did she use? (a wider choice of colours is inferred here)
3) Who made it? Did you? OR "Was it me or you?" (in this case, who is the subject of the question and does not require an auxiliary)
You can omit the wh question word and ask a yes/no type question.
Auxiliary + subject + infinite
- "Did you use blue or green?" asked Maria.
- Maria asked, "Did you make it?"
If you wanted to use whether you have to rephrase your sentence. Note that the following are not questions. There is no question mark at the end.
- Maria asked whether she used blue or green.
- Maria asked whether [name] made it or not.
If you really need to make questions with whether then the following is acceptable
- Do you know whether she used blue or green to make her scarf (it)?
- Did you find out whether it was me or her who made it?
Best Answer
Ordinarily you use the 'declarative' only when the question is 'echoic' - that is, when you are asking for confirmation or clarification of what you have just heard, often explicitly echoing the language your interlocutor has employed. In most cases you will stress a specific term which you find incredible or did not hear clearly.
And in these circumstances, where you are questioning what you have just heard, you will not use the ordinary interrogative form unless you stress such a term—otherwise your interlocutor is apt to respond “Weren’t you listening? Didn’t I just tell you that?”
But if you are not responding to what has been said, if you're just asking for information, you will ordinarily use the interrogative form.