What is meaning of the sentence 「夫非盡人之子與」?
夫 is a particle that you can ignore in this sentence.

Here, 非 is a negation, in this case as part of a rhetorical question with 與: Is it not? (or, in this case: Are we not?)

盡 in this text means all.

Now, 人之子 belong together: sons of men.

Finally, 與 is a final particle marking a question, like 吗 in modern Chinese.

The translation of the sentence is: “Are we not all sons of men?”

This is a translation without context, of course. I’d have to read the rest of this Mengzi passage to give you a better one.