You may want to see if he will voluntarily deed the house to you.
If you get the home, you can then evict the tenant.
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I agree that you should see if your son will give you a deed to the property. If he doesn't want to give you a deed, perhaps he'll agree to give you a lien on the house to cover your investment (for tax sale redemption and future taxes/insurance). If he won't give you a deed, maybe he'll appoint you as his agent so you can evict the tenant.
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