Sentence examples for of all of them from inspiring English sources

"of all of them" is correct and commonly used in written English.
It is typically used to emphasize a comparison or to make a superlative statement. Example: Of all of them, she was the quickest runner on the team. This sentence emphasizes that out of everyone on the team, she was the fastest. Another example: I have tried many desserts, but that was the best of all of them. This sentence emphasizes that out of all the desserts the speaker has tried, this one was the best.