I would check around. If your sister is willing to add you to the title, it could cost well less than $500. I normally charge $200 for this, in Michigan. The problem is...you cannot force your sister to do this. She is free to let the house be foreclosed if she wishes. That is your biggest problem.
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As Mr. Frederick mentions, feel free to shop around. However your sister has the right to do as she wishes.
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If this is the case there is no reason to keep paying for the upkeep. Tell her you will not keep paying if she does not transfer 1/2 of the property to you. By the way, you are not entitled to deduct the taxes you pay on the house on your individual tax return. Also, if she does agree you then are going to have to determine which form of joint property to use; joint tenancy or tenancy in common.
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