Yes, for the past perfect. "He had sent the letter."
"Will be sent" is correct.
You have sent is correct.
"Have sent" is grammatically correct.
"Have it sent" is correct.
I have sent, he/she has sent, we have sent, they have sent.
"Will be sent" is correct.
You have sent is correct.
"Have sent" is grammatically correct.
"Two of them have sent" is correct usage.
"Have it sent" is correct.
I have sent, he/she has sent, we have sent, they have sent.
Yes, it is correct. You are correct to use "who" and not "whom" because "who" is the subject of the clause "who has sent him."
"I was sent the present" is correct, passive but correct. The first sentence needs "to" before "me" to be correct--"The present was sent to me."To make the sentence active, identify who sent the present. For example, "Billy Bob sent the present to me."
It would be correct if you would've said, "All of them have sent a response," or, "All of them have sent responses."
Mail you had sent earlier is correct.
Yes!it is correct to say homework was sent home.
Both are correct, the only difference is that "has sent" is in present tense and "had sent" is in past tense.e.g. Mike has sent me a letter. (present tense)Mike had sent me a letter. (past tense)