Short answer:
The two characters only need to be at the same site.
Explanation:
During the organization phase, the resource player may transfer an item from one character in a company to another character in a different company, as long as both companies are in the same site. This ruling is upheld by all rulebooks except for the rules summary of the Balrog and Challenge Decks.
Note that this ruling should be considered a clarification to the TRANSFERRING/STORING ITEMS section from the MECCG Rules Summary of The Balrog and Challenge Decks.ICE Rules Digest #515 Q6 also endorses it:
QUERY 6
Anthony Perez-Miller
Van Norton wrote:
Situation: I arrive with company A at a Haven with company B. Can i transfer an item to company B during my next org. phase and maintain same companies (A / B) at the end of my org phase? (i.e. can a character of company B join company A for the transfer and join company B after the transfer of the item?)
R: The items can be transfered without altering the companies.
What if one of the companies is bearing a Fellowship? Prior to this, any such transfer meant that the companies would combine, and then split again, meaning that Fellowship would be discarded. I assume that the same would hold for the Orc version of Fellowship (Swarm of Bats, or the like). Has there been a change when I wasn’t looking?
Nothing has changed as far as I know. The rules say that characters must be at the same site to transfer items. It doesn’t not say they have to be in the same company. Of course, the only time you can have two companies at the same site without them combining is at a Haven, so maybe that’s what you are remembering.