Terminating lease mutually

[Morgan Stone]

We recently bought a duplex to “house hack” and one side was filled with a year lease ending in October of 2020. 
My husband’s grandfather is looking to move closer to family due to health issues and asked if he could move into the side that currently has the tenant. 
Can I ask the tenant to move out even though his lease isn’t over until November?

Is is a bad idea to rent to my husbands grandfather? He understands he will have to pay the full rent because we are young and can’t afford to lose the income from our rental.