yes
It depends on the context. "He saw" is the correct past tense form, while "he see" is not grammatically correct in standard English.
All it needs is a question mark. Have you had lunch? That is grammatically correct.
The correct phrase is "I saw it." "I seen it" is not grammatically correct; "seen" is the past participle form of "see" and is used with a helping verb (e.g., "I have seen it").
No, I sould suggest "What do you all expect?"
Yes, as the object of a verb or a preposition: I saw Bob; I saw her; I saw Bob and her. Some people think "her and Bob" sounds better, but it is not any more correct. There is nothing wrong grammatically with the construction 'Bob and her' as the object of a verb. Whether it sounds better or worse than 'her and Bob' is a question of usage or taste, not of grammar.
No not at all
yup...
"You could not have been" is grammatically correct. "You could not have been at the cinema last night, because I saw you in the park."
No, the phrase "of which we are all" is not grammatically correct. It would be better to say "of which we all are" or simply "which we all are."
Yes, the sentence "you saw your uncle and aunt come out" is grammatically correct. It describes the action of seeing both your uncle and aunt exiting from a place.
Short answer : Yes and not impolite at all, as suggested below. This is to be handled by you grammatically correct? requires inverted commas to be correct. It should be written as: "Is this sentence "This is to be handled by you." grammatically correct?" The sentence is correct but not very polite; it would be simpler to say "You are to handle this"
"Not like that" can be grammatically correct, depending on the context.