"Whom" is the objective form, and "who" is the subjective form. Use "whom" where you would use "him" or "her"; use "who" where you would use "he" or "she". Examples: I wondered who would be there....
should have: You should use should have in a sentence as past tense like "You should have done your chores." I agree with that as: This is used when you are talking about an event that took place...
"I should have had better information before jumping to that conclusion." SHOULD HAVE indicates that something was expected, but didn't happen. SHOULD HAVE HAD indicates a better outcome could or...