grandparents

Receiving rental from a house that was purchased with haraam money

Q: My grandparents won a lottery of 1 lakh rs around 20 years ago. They then added some amount to this lottery amount (around 35K rs) and purchased a home. Thereafter, one of my family members lived in that house. Presently that house is on rent and we receive a rent of around 10K rs per month. I came to know that lottery is haram. So what should be done now?