This sounds very complex, and it appears you are having difficultly acquiring the evidence you need to prove your case. Keep in mind that your case is not about proving the guardian unfit, but about proving yourself as fit so the guardianship ends. You have to get a lawyer. After two years, it does not appear you are going to be able to do this on your own.
Responses are for general information purposes only, and are based on the extremely limited facts given. A consultation with an attorney experienced in the area of law(s) indicated in the question is highly recommended. Information and advice given here should not be relied upon for any final action or decision, as the information is limited by its nature to the question asked and the fact(s) presented in that question. THIS RESPONSE DOES NOT CREATE AN ATTORNEY/CLIENT RELATIONSHIP, particularly considering that the names of the parties are unknown.
I agree with Ms. Whitbeck. These are always fact-intensive cases and you would do well to have an attorney working for you. The judge must look at numerous factors in assessing the "best interests of the child" and the attorney will know best how to present those - and rebut the arguments of the guardian. And the more times you try to terminate the guardianship the more it will look like desperation. An attorney is usually worth their weight in these sorts of matters.