If your uncle truly had a legal (court ordered) guardianship of your grandmother she had no legal capacity to transfer the property and the Deed is void.
However as you state there is actually more though. Consult with an experienced real estate attorney.
I agree with the previous answer and you need to take all of your documents and evidence to an attorney locally many offer free consultations and will sort through your options quickly. If the taxes are not paid there will be a tax auction.
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You should have a qualified local attorney review all the documents and go over your options sooner rather than later. Competing POA's can be confusing and muddy the water with regard to transfers and division of responsibilities.
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You need to hire an experienced probate attorney who can gather the relevant facts and documents so you can then receive meaningful legal advice. The answers here are not going to solve your problem.