If your grandfather is deceased, your aunt's power of attorney is now invalid. If your grandfather is not deceased, the power of attorney is valid and your aunt can follow the powers granted to her. A trust can be revoked, but if it has been funded - such as deeding a house to trust - the assets should be taken from the trust and put back into the grantor's name before revoking the trust. If the trust has not been revoked, the trust should be followed for assets that are in the trust. For assets that are not in the trust, the will should be followed. You can check the public records of the county where the house is located to see if the deed is in the name of the trust. If it is still in the name of the trust, the trust will be followed regarding the real property when he passes.
I assume grandfather created the trust in '98 as a foundation for his overall estate plan and not just for a single asset or single purpose. Your grandfather has to revoke the trust for it to no longer govern the post-mortem disposition of property held in it. In writing would be a good idea, although it can be implied from his conduct, and there is no reason he couldn't state the revocation in the new will. An will by itself wouldn't ordinarily be determinative as to revocation of the trust, so he would have had to custom draft a specific statement of his intent to revoke the trust. It would, however, revoke the pour-over will he should have signed when he set up the revocable trust.
If a written statement by him was clear enough, it would probably be enough to overcome the contradictory evidence posed by the title to the house still being in the name of the trust. In that case, a court would probably conclude the trust was dissolved and the house distributed to him as owner, if not title holder. If so, it would pass under whatever his last will is. Without a clear writing, however, it is quite possible the house would remain in the trust and pass according to its terms. Although it is common for someone with a revocable trust to have only a pour-over will into the trust, it is possible to have a trust for some assets and a will going in a different direction for the rest.
The power of attorney typically only grants her authority over assets not in the trust and unless specified, she would not have authority to change his estate plan. The power of attorney terminates at grandpa's death.
If this sounds confusing, the fact pattern you describe sounds like a tangled mess that will be expensive and difficult to untangle after the fact. Right now there appear to be enough uncertainties to make it near impossible to arrive at certainty about his intent.
Is your grandfather still legally competent? If so, maybe you can clarify the situation and his intent with him, or, if he had an attorney do the trust the attorney can contact him and try to figure out what's going on.
This all may be innocent, or the aunt may be exercising undue influence. The facts do not indicate any foul play. If you develop concerns, you should explore whether OH has an adult protective services agency and see if they would intervene. Or, consult a competent local elder law attorney to explore whether a guardianship/conservatorship should be sought in the courts. But I stress that your description of the facts does not necessarily imply any foul play or abuse is going on. It's possible grandfather just changed his mind, whic is his right as long as he retains capacity to do so.
In general a will and trust are two different things. Your grandfather's trust would govern all the assets in the name of the trust such as his house. The will would govern any assets that are just in his name alone. Any joint assets or assets governed by beneficiary designation will be governed by the beneficiary designation.