Your dad crawling up the stairs is helping to fend off muscle atrophy. There's a risk of course. Falling down the stairs could lead to death after complications. But it's not as out-right bad as you might assume, and crawling reduces the fall risk a bit. Falling is a risk even with normal walking. But if you don't have some movement in their life, they degrade faster and die sooner. There is risk from all choices
classic hackernews response
Like seriously if your Dad is crawling up the stairs, he has already decided that He Will Keep Using Both Floors Of His House Until He Physically Can't Anymore. Apart from completely destroying his agency, you are not going to stop this.