Without getting into the merits of your position, since more facts would be needed to determine whether you are right or not and to determine where in the probate process you are, I will say that in general terms and assuming you have some articulable facts on which to base your fears, you would need to obtain an injunction from the court to prevent a sale. You really need to contact a lawyer to ensure that whatever rights you have are preserved.
In addition to Attorney Bashara's answer, which I agree with, I will simply add that, from what you have said, your father did a very poor job of setting this up, for the property to go to you. It is pretty clear that he should have used a lawyer and did not. That being the case, his home-made estate plan is likely going to cost you the house. I hope that I am wrong and you are able to persuade the judge of your position. But this is simply not how it is supposed to be done. He *could* have planned his estate in such a way as to protect you. Because he apparently did not, you are at the mercy of the court and your stepmom.
I think it is unlikely she will try to sell the home before the hearing. It would be too easy for you to complain to the court. Because of the hearing, she is clearly on notice of your potential claim.
You absolutely need a good probate lawyer on your side in order to present your case in a manner most likely to garner a positive result. Your lawyer is going to have his/her hands full.
*** LEGAL DISCLAIMER I am licensed to practice law in the State of Michigan and have offices in Wayne and Ingham Counties. My practice is focused in the areas of estate planning and probate administration. I am ethically required to state that the above answer does not create an attorney/client relationship. These responses should be considered general legal education and are intended to provide general information about the question asked. Frequently, the question does not include important facts that, if known, could significantly change the answer. Information provided on this site should not be used as a substitute for competent legal advice from a licensed attorney that practices in your state. The law changes frequently and varies from state to state. If I refer to your state's laws, you should not rely on what I say; I just did a quick Internet search and found something that looked relevant that I hoped you would find helpful. You should verify and confirm any information provided with an attorney licensed in your state.
There is not much to add to what my colleagues have stated. You need to go find yourself a local probate attorney that can step into the mess your father created for you. This situation is not uncommon, where home-grown estate planning goes awry. If you are able to get this successfully resolved, hopefully you will see the merit of setting up an estate plan, though an attorney, to accomplish your goals. Good luck
When responding to questions posted on Avvo, I provide a general purpose response based on California law as I am licensed in California. In reviewing my response, you are specifically advised that your use of, or reliance upon any response I provide is not advisable. I do not have all relevant background details or facts related to your issue / matter, thus I am not in a position to give you legal advice. Further, your review, use of, or reliance upon my response does not establish an attorney-client relationship between us nor does it qualify as a legal consultation for any purpose. For specific advice regarding your particular circumstances, you should consult and retain local counsel.