What responsibility does a lender incur when federal or property taxes are not paid and liens are put on the property?

i'm not sure what federal tax liens you mean.  A mortgage usually has first priority. That means that if there is a mortgage on the property, and the amount of the mortgage exceeds the current fair market value, (also known as being "under water") then the federal liens takes second place after payment of the mortgage.  The mortgage company usually pays the property taxes.  If the property is "run down" the mortgage company will not pay for repairs.