Right of redemption - owner financed mortgage went to tax sale

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There is a group of houses I am interested in purchasing that was sold in 2012 via owner-financed mortgage.  Per the warranty deed, the mortgager was responsible for paying the taxes on the property.  The mortgager stopped paying his mortgage in 2013 (approximately one year after signing mortgage) and also failed to pay property taxes.  The properties went to tax sale and the state of Alabama acquired the properties in 2015. 

If I was able to purchase the promissory note from the original mortgagee, would I have the right to redemption of the houses?  Would I have to foreclose on the mortgager who has not paid since 2013 or does the tax lien trump foreclosure?  I am trying to figure out the best route to go in purchasing these houses. 

Any advice would be helpful.  If anyone needs more info, let me know....this is my first time posting!

Anna