You're a few years older than I am, shack. They had stopped using the word predicate in English class by the time I got that far in school.
Who did what to whom is grammatically correct. It's consistent with my rules of thumb Who complies with he, she or they. Whom complies with him, her, or them.
When I learned that, 'they' was always a non specific plural pronoun; now it can be an Alphabet person using the 'Royal We' personally.
I tune out anyone other than Queen E and her descendants, (other than Harry and Andrew), who uses the 'Royal We' instead of I. If you ask one of them to define the "We" to which they are referring, they'll never give you a straight answer, but they'll usually smile.
I don't think anyone got my joke in post #8. Update: roadhog did.