Duplex shared lawn care/snow removal percent of responsibilities

[Wendy Busa]

Soon to be new landlord. The unit is basically a single family home  2800 sq ft and 950 sq ft, mother in law apartment. Current tenants take care of large shared yard and driveway. The current lease is a joke and does not specify anything. Drawing up new lease for when the old one expires.

I am adding specifics to the lease and wonder how I should divide up the lawn care/snow removal. Would it be fair to make the larger unit solely responsible for all of the lawn and driveway? The tenants are mother and daughter. They plan on staying.

Any ideas would be appreciated. Thanks