Joang, The non Medical requirements are just that they have to make sure he has worked enough quarters to qualify and that he has worked 5 out of the last 10 years before you applied. If he meets these requirements then it is a done deal, he will be approved.
They are pretty strict, but Alzheimer's Disease should be a sure bet for being approved. Sid has severe diabetic neuropathy that makes it impossible for him to stand or walk for more than a few minutes. 3 years ago, when that started, we were discouraged from applying because everyone said that SS would just say that he could get a "sitting down" job. But when he was diagnosed with Alzheimer's on top of the physical condition, all the neurology reports said that he was incapable of learning something new or remembering anything he was told, and that he should not be allowed to make any major financial or medical decisions. That sealed the deal for SS, I guess. We still haven't heard from them about the non-medical requirements, but I can't imagine that being a problem.