Regarding your question about the following sentence:
“Of all the people visiting hospitals, there would be one or two who would need a wheelchair.”
I often see such usage of the preposition “of,” but I think it’s grammatically wrong.
The phrase “of all the people” means “a possession or characteristic of all the people” in the collective sense. We can find out right away that the usage of “of” is wrong when we move that phrase to its usual position in such sentences, as follows:
“There would be one or two of all the people visiting hospitals who would need a wheelchair.”
See the glaring logical contradiction in the fusion of “one or two” and “of all the people”?
The preposition that would yield the correct sense is, of course, “from among,” meaning that the “one or two people” specified in the sentence belongs to the totality of all the people visiting hospitals:
“There would be one or two from among all the people visiting hospitals who would need a wheelchair.”
or, in the positioning of that phrase in the original sentence:
“From among all the people visiting hospitals, there would be one or two who would need a wheelchair.”
Conversationally, however, “from” can be dropped from such phrases and still yield the same meaning:
“Among all the people visiting hospitals, there would be one or two who would need a wheelchair.”
Now to your question: Would it be correct to change “of” with “from” in such sentences?
Let’s take a look at what happens when we do that:
“From all the people visiting hospitals, there would be one or two who would need a wheelchair.”
“There would be one or two from all the people visiting hospitals who would need a wheelchair.”
Using “from” alone obviously doesn’t work. This is because “from” is a function word that indicates the source, cause, agent, or basis of something, as in “we can infer from her statement,” “an e-mail from a friend,” “took a part-time job from necessity.” It doesn't yield the sense of “belongingness” intended in that sentence.
By the way, when the article “the” is dropped from the phrase “of all the people,” the meaning of that phrase changes altogether. It becomes the idiomatic expression “of all people,” which means “more than anybody else,” as in the following sentence:
“Meteorologists of all people should know better about the weather.”
