Yes guests' is the grammatically correct possessive plural of guest.
For example, "Take the guests' coats and put them in the bedroom."
'She does not have her book' is grammatically correct.
He, you and I is not grammatically correct. The proper way to say this is you, him and I.
Yes, soonest is correct grammatically.
"Not like that" can be grammatically correct, depending on the context.
Yes! That is grammatically correct!
Yes, 'for free', is grammatically correct.
Yes it is a grammatically correct
Currently we have is grammatically correct.
Yes it is grammatically correct but it is ambiguous. Were the wedding guests wearing green glasses or was the ice tea served in green glasses? In the first case the sentence would be better to read "Iced tea was served to the wedding guests who were wearing green glasses." in the second case It would read "Iced tea was served in green glasses to the wedding guests."
This is not grammatically correct. The correct form is 'you do not know', or the abbreviated 'you don't know'.
Yes, it is grammatically correct.
'Rhoda's crazy' is grammatically correct.