If the mortgage is in your nephew's name and you are paying the mortgage then you are essentially paying for your nephew's home. You do not have a legal right to own the home if your nephew does not want to voluntarily give you the right. If he is the only one on the deed it does not matter who is making the payments.
The only way you have a legal right to the home is for him to quitclaim to you the property. However, he cannot quitclaim to you the home unless he get permission from the Mortgage company. The mortgage company has a due on sale clause on the mortgage. This means if the home is transferred then the mortgage company can demand payment of the entire mortgage immediately. The only way to transfer the property and avoid the due on sale is to get permission from the mortgage company.
Once the property has been quitclaimed to your name the taxes will be in your name as well.
I cannot provide you with legal advise. I have provided you with information about the law related to your question. My answer, and any information that you find online, should not take the place of having a consultation with a lawyer in your area to advise you regarding your specific issues.
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