As the title, says, I have a 99 Odyssey, and the key won't turn. The steering wheel is locked, and the van is in Park.

Yes, I tried, wiggling the wheel back and forth while turning the key - no luck.

I tried all 3 keys - no luck.

I jacked up the front end to take pressure off the steering column, then played with the key - no luck.

I free'd the shifter to put the van in neutral, then played with the key - no luck.

I think it is probably a problem with the key assembly/tumbler/etc.

Any ideas?

You got it, replace the mehanical portion of the assy in its entirty.