Search google for Indiana legal code and you will probably get a good start. But from what I have read, you have to be several years delinquent before they will seize your property. It depends on the state but some will auction the property and some will sell it for the back taxes.
The fellows with the leins could go to court and force the sale of the house to get paid for the leins. The guy paying for the house on the contract didn't even have to be notified.
The situation got pretty nasty during a period of high growth so the legislature acted to clean up the problem.
Subsequently the state has made other changes, re-codifications, reorganizations of the pertinent statutes, and imposition of various state supreme court decisions on top of all of that.
I'm not a lawyer but as long as I had any close relatives there owning a house I tried to keep up with Indiana statutes and decisions.
Finding out how to buy a property for back taxes in Indiana is not all that straightforward a deal.
If I had to help someone out these days I'd read the statutes and decisions quickly THEN CALL AN INDIANA LAWYER who specializes in titles and taxes.