Make sure you do not have the game paused when you are trying to drop stuff.

If you can not summon a doll and off-load a bunch of stuff onto it (anything but quest or unique/set items), try transferring enough weight to one character that the other can move out into a more open area (or just enter the BF).


I don't believe you can give a teleporter stone to a merchant.
There is a fixed teleporter stone in act 1 that you can use but not take, and a set of teleporter stone to find in act 2 (which you keep until the start of act 4).
If you found the first one in act 2, click on the second teleporter stone on the ground (drop and use it if necessary) to teleport back to the pit where the first one was, then click and drag that teleporter stone into your inventory. Use that teleporter without dropping it (either through the secondary skill menu or clicking on it in your inventory) to get back above ground, then pick up that teleporter.