First rental property question

[Caden Fox]

My grand parents are planning to sell me a house they currently have rented. We plan to close in early January 2021. I plan to rent it out as well. I would like to keep the current tenants in the property provided they pass my checks. My question is how much advance do my grand parents need to give them to leave the property. I am in Tennessee. Also I understand COVID has changed a lot of rules. Any new guidance that I should be aware of? Thanks