Currently, in a multiplayer session only the host can control/converse with/itemize henchmen that have joined the party. And from everything I've read, this is intentional. I can understand this protective arrangement in a drop-in/drop-out co-op setup - it limits what a random player can do in the host's game (and I realize there's currently a bug that makes this very random).
That said, some of us are playing this game co-op with family or real-life friends. And the expectation is that we are all equal partners within the game-world, rather than merely tagging along and playing the role of the host's sidekick in the host's personal playground.
I strongly believe either player should have the option of controlling the henchmen. We should have the option of splitting them up, or having two of them follow one player - either player. We should both be able to have conversations with them. We should both be able to determine their equipment loadouts and character advancement. In short, both players should have the same options a host has. The host should simply be providing the "server" to play on and nothing more.
While I feel it's the host's responsibility to be more careful about who they invite to their game, if you really feel the need to protect the host then at least provide the host with options in this area to disable the limitations on henchmen.
Thanks, all!