It means "live ones."
It can be a literal phrase (people who are alive), or it can be slang.
In terms of slang, Wiktionary provides three senses in its definition:
1 (idiomatic) Someone who is easily fooled, victimized, or ridiculed.
2 (idiomatic) Someone who is eccentric, nonconformist, or otherwise peculiar.
3 (idiomatic) A person, thing, or situation which is particularly interesting, noteworthy, or urgent.
For example, you might hear, "Oh, we've got a live one!" from a comedian on stage in response to a heckler.
In the short passage you quote, I believe (if memory serves) that the crowd is composed of ghosts, with the trio being the exception. So, in this case, the phrase would be meant literally.