According to formal grammar, who is used in the subject position, while whom is used in the object position. In modern English there are many speakers who rarely use whom at all, using who in all contexts; today this use is broadly accepted in standard English.
I think - Please take care of whoever is waiting - is better.
This sentence is grammatically correct.
Yes, it is.
You had not taken that into account. Would be the grammatically correct version of that sentence.
Der Junge ist rothaarig is grammatically correct.
It can be, like in the following sentence. There were many firsts in this historic week.
"That was wrong" is a grammatically correct sentence.
This sentence is not grammatically correct. For the sentence to be grammatically correct, the space between "in" and "to" would have to be removed. Therefore the sentence should read "They are into skating."
The sentence is grammatically correct.
yes
The sentence "Rhoda's Crazy" is not grammatically correct. It is missing a verb to make a complete sentence.
The sentence (not sentance) is grammatically correct
Yes. "I do not like people" is complete and correct, albeit anti-social.