It is possible to transfer items between inventories, but a bit clunky.
Click and drag the item up to the character avatar image on the inventory screen, then click the arrows to swap chars and drop it in. Items will "swap" if you drop an item on top of another one though, so make sure you drop it to an open slot unless you actually mean to swap them.
EDIT - sorry, didnt spot your edit to say you'd found it lol, apologies.
Also for stealing items, I've found the cursor/interaction cogs/etc do turn red if I'm about to steal something... my problem is that I often clip something by mistake and end up attempting to steal something I never intended, or get spotted mid move to the item and don't have enough time to cancel the action. As a result most of the npc's in town on my save have me at at least -10 rep
