It has been a godsend for our family that my parents were able to move into a retirement community that offers a progression of care. My Dad has progressive supranuclear palsy and requires relatively constant care, while my stepmother is better able to live her life with some of the chores/maintenance handled by professionals.
I don't know if there are eldercare places that let potential residents try retirement living/assisted-living out for a month or so, but the community and amenity experiences can yield a flowering of life after elders have though that they were condemned to almost home-isolation by their mobility.
The fact that your Dad has the fortitude to crawl up a flight of stairs every day is truly admirable -- the key is helping him find his way toward a situation where that kind of effort is optional and safer, rather than a requirement and a risk. As @crispyambulance says in a nearby thread, falls are the big risk.
Good luck -- none of this is easy, but with experienced assistance, it need not be a series of unexpected calamities.