1. He has the least money of all his classmates.
2. He has the least money of all the boys in his class.
3. He has the least money of all the boys in his classroom.
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Are they all grammatical?
Is #1 logically incorrect?
Yes, all are grammatically correct, and all three are logically correct. :)
Yes, all three are grammatically correct, and are logically correct.
In Sentence 1, 'all his classmates" doesn't include the subject 'He.' So is this sentence logical or correct?
For sentence 1, another (maybe better) way to phrase it is this ~~> He has less money than any of his classmates.
Yes, all three sentences are grammatically correct.
Regarding the logical correctness, sentence #1 is not necessarily incorrect, but it does not provide enough context to determine if it is logically correct. When it says "He has the least money of all his classmates," we do not know whether all his classmates have different amounts of money or if they have the same amount. Without additional information, we cannot determine if he truly has the least amount of money.