2 players stand facing one another with a 2 handed weapon in hand (2 handed melee weapons WILL work with this method) and at least one player with enough room in their inventory to accommodate said container. The container is then loaded with the items to be duplicated and dropped so that both players have access to it via the vicinity. Both players, at the same time, then drag the container over their weapons which are in the "hand" slot. By doing this, it will place the container in the hands of both players while both dropping their weapons to the ground. One player then drags the container to their inventory. This will remove the container from the OTHER players hand and place it in the others inventory causing one container to appear in their hand and one in the same players inventory. The player with the now duplicated container then logs out and back into the same server. Upon logging in, both containers are accessible along with the items inside of them.
here is a youtube link to a video tutorial of the above issue (note: This is not my video nor am I affiliated in any way with the individual who made this video.)
https://www.youtube.com/watch?v=uXYRfUtjoAA