"Something" and "someone" refer only to one thing or person. If you want them to be plural, just say "some things" and "some people" respectively. In both cases, "some" is optional because they are plural indefinite. "Everyone" and "everything" already refer to everything, so logically they can't be plural if they're already singular. If you really want them to be plural, you can say "all things" and "all people". These mean the exact same thing.