If a person is sitting in their vehicle and refuse to get out can the police force them out for the repo man?

Hell no, Unless they have a "writ of replevin" which will be delivered by the sheriff or other law officer. Without that, your invincible, unless you assault the repo man or other. Just hop in and shut up until they call the police, then explain to the officer whats goin on. Stick to your guns, because without a court order and you getting arrested for being an idiot, then the police are simply there to keep the peace. Just because he repos for a living, doesn't mean he's got power.