No, "Is you are most invited" is not correct grammar. A more grammatically correct phrase would be "You are most welcome" or "You are invited." The sentence structure needs to be adjusted for clarity and correctness.
You and your family are invited.
That is grammatically correct.
"Both of whom" is correct grammar. It is used when referring to two people. For example, "I invited John and Mary, both of whom attended the party."
All staff are invited would be considered correct in English usage. American usage may be different.
"You are most welcome" is correct grammar.
It is correct to say that you are invited to a particular event, not invited for.
No, "will be had" is not a correct grammar. The correct grammar would be "will have."
Yes it is.
No, it is correct grammar, not a correct grammar.
No, the phrase "at the most earliest" is not correct grammar. "Most" and "earliest" are both superlatives, so using them together is redundant. The correct phrase would be "at the earliest" or "at the most."
The correct grammar is: "Are those correct?"
sunnysunniersunniest