0 I'm not sure of the grammatical specifics, but, as a native speaker this sentence sounds correct to me. Replacing "THEIR" by "HIS" is rarely used, as I see it, and it implies that only males will be in attendence. 'EVERYBODY' is ambiguous and doesn't imply, as if it were replaced by "ALL THE MEN", that males will be the only gender in attendence.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.