Cost Basis for "second home"

In 2017 I took ownership of my parents home for estate planning purposes with the idea that they would live there until they passed on and then I would sell it.  In 2021, my father passed and my mom didn't want to live there anymore.  I therefore sold the house and gave her the money from the sale, which she then used to purchase another home.  Now, as I try to do taxes for 2021, and not wanting to have to pay several thousand dollars in taxes for a home that I literally received $0 from the sale thereof, I am trying to figure out what to do.  Is my cost basis for the home $0 because we literally just transferred it over to me?  Is it the market value of the home at the time of the transfer?  Am I entirely missing the boat and not thinking about something I should be?  Thanks in advance for any and all advice.