3-Family Residence

Here's the idea: There are three tenants (I'm likely one of them). House, Room, Apt.

House

2 bedrooms, 1-3/4 bath, full kitchen, full laundry - ~1500SF

Keys: The front door at the living room, the door from the breezeway to the house (where the laundry is now). Combination to the breezeway door (because there is a zero-step ramp to that door). Garage door opener for east side.

Access to the backyard and the small deck through BR1 and the Breezeway. Maybe a new slider in BR2 (over the basement stairs). 

Can access the stairs and the Room/Apt laundry, but doors to Room and Apt are locked. Hall opens onto the garage.

Room

1 bedroom, 3/4 bath. Hot plate and refrigerator. - ~200SF

Access to the large deck and the backyard. Tankless water heater. Key to the door at the deck. Combination to the breezeway door.

Access to laundry facilities up the stairs.

Parks on the street or on the verge of the driveway.

Apt

1 bedroom, full bath, minimal kitchen - ~500SF

Combination to the breezeway door. Key to the upstairs Apt. Garage door opener for west side.

Apt has a living/dining room with an alcove kitchen, a small bedroom with en suite bath. Outside in the hall, a stacked washer/dryer to share with the person in the Room.

Combined Tenant

A single tenant--a couple with a teenager, or a couple with an aging parent--could rent both the Room and Apt. 

2 bedroom, 1-3/4 bath, minimal kitchen, laundry - ~700SF

Large House

The other alternative is a single occupant:

4 bedrooms, 3-1/2 bath, two kitchens, two-car garage, step-free entrance = ~2200SF

Common Space

The stairs, the breezeway, and a hall outside the garage become common, wasted circulation space. It's about 240SF all told. Not great, but very flexible.