"The man is in there."
Translation:A férfi ott van bent.
"bent" means "inside" without specifying inside what. "ott bent" means "in there", referring to some concrete place. So "a férfi bent van" means "the man is inside", and this may work if it's clear from context where he is. But it's not a translation of "in there", which is more concrete.
(Finally, the order you gave, "a férfi van bent", is also grammatical, but it puts a strong emphasis on the man, as in "THE MAN is inside, not the woman". This is only appropriate when you want to stress this new or contradictory information. But you'll get to worry about this later.)
It does not indicate moving at all. I know it sounds weird, because "oda" alone does but try to disregard that fact.
A férfi ott van bent. A férfi odabent van.
These two mean the same exact thing. To me personally, the latter one sounds a bit more dated or just a tad bit formal in a way and the former is kind of more basic. But you could absolutely say either of them and both are used in everyday speech.
It doesn't sound good to be honest. Maybe because you are clustering a slightly redundant piece of information. Maybe because location+van acts a bit like a phrasal verb on its own but only with one location information at one time and the other gotta go somewhere else... or it's just like a common phrase without further explanation.