Which in-law living situation would be best

So I’m planning to have my wife’s parents move in from China sometime next year. I’m trying to decide which setup would be best.
While some options may be more expensive, money is not a deciding factor.
They are in their mid-60’s, active and healthy for their age.

Old Garage Apartment - Only about 8 years old, it’s a detached garage with an unfinished workshop ground floor, and a ‘finished’ living space top floor. About 1,200 sq feet.
Pro - most privacy for them and us. Low cost/work to be done. I think it’s a really cool space
Con - Stairs. Loss of a workshop.

New Garage Apartment - An addition I’ve been planning for a while. An attached basement+ground floor garage. Probably also 1,200 sq feet. Could scrap the “garage” portion completely if I still had my detached.
Pros - Wanted it anyway. Attached. Could be designed/built with elderly access in mind.
Cons - Not a lot of privacy. Most expensive option.

In-house Suite - Already have a 2 bedroom 1 bath section of the house I was going to renovate into a living/guest space.
Pros - No stairs. Minor renovations and updating. Unused space I wanted renovated anyway. Most accessible.
Cons - Shared entrance, not a lot of privacy. The smallest area.