Can you buy a home for back taxes and tell the owners that they are signing an IOU one of the owners was in a hospice after 4 strokes and his wife was told that they were signing an IOU. They have paid the money he lent for them for the back taxes and they did not know that they had even signed an Quitclaim.

First its not a good idea to piggyback your question on someone else's. This can lead to confusion. You should start a new thread. So I've moved your question to its own thread.

That smacks of fraud. I would contact the police.

First you can not buy someone's home by just paying the back taxes, you can go to a court sell and buy property at a tax auction. There depending on state law they may own it or merely have a tax certificate which can be redeemed.

This sounds like a fruad, it sounds like they claim to have paid the taxes and wanted a "loan" ( not a IOU) paper signed saying that you owed them the money for the back taxes.

But a quitclaim deed needs to be notorised so you would have had to go in front of a notory and have the sale notorised to be valid

Someone is cheating or trying to cheat you, as noted call the police, check with the courthouse as to if there has been a new deed recorded and if so, hire an attorney.