It is not off the table as an option. My property is such that if we built a granny unit in the back, there is a separate driveway entrance and you would barely see it from the house. So there is a lot of privacy. I think the local ordinance limits the size to 600 sq. ft., but we lived in an apartment that size and it was fine.
The main motivation for the granny unit is preserving our standard of living, make joint custody easy -- hey kids, go visit your mom in the backyard . About the MR, frankly I'm starting to feel like I'm done.