For part (a), the answer is yes. If the natives are both knights or both knaves, they will both answer "yes" to the question. If one of the natives is a knight and the other one is a knave, they will both answer no to the question.
For part (b), there is always an odd number of knights. If A is a knight, then the other two are both knights or both knaves, because they are the same. If A is a knave, the other two are one knight and one knave, because the knave is lying. In both cases, there is an odd number of knights.
For part (c), you can use the question in part (b). "Are the other two the same type?" Using this question, if you get yes, no matter if the one you asked is a knight or a knave, there are an odd number of knights, which answers the question. If the person says no, then there are two knights.
For part (d), B is a knave, and A could either be a knight or a knave. The statement "B is a knight is the same as I am a knave" sounds confusing. Just split the statement into two parts: "B is a knight" and "I am a knave". The words "is the same as" tells you that the true/false component of each of these is the same. If one is false, the other is false. If one is true, the other is true. Therefore, if A is a knight, both parts of the statement are false, and the middle words "is the same as" makes the statement as a whole true. If A is a knave, the true/false component of each of the statements is different. "I am a knave" must be true and "B is a knight" must be false. Therefore, A can either be a knave or a knight, and B is always a knave.
You have exactly the right idea. You force the liars to make two negations. This question works just fine, as will others, as long as they are "honest" liars.
Best Answer
The key is to separate what they would do and what they say they would do.
The knight would say "Yes, I always tell the truth." and thus since the knight always tells the truth would say "If you asked, I would say 'yes'." So far so expected.
The knave would say "Yes, I always tell the truth." but since the knave always lies would answer this question: "If you asked this question, I would say 'no'."
The knave has to lie about his lying, and so tells the truth.