Who do I contact to pay off balance of Medicaid lien on home in which we now reside?

Your question has several layers.
The first item is when a lien is recorded there should be contact information on the lien allowing you to get a pay-off number.
Second how the pay-off will affect the status of your mother-in-law medicaid account is something you will evaluate with an attorney.
finally, The lien represents equity taken from the value of the property including improvements.

Good Luck