For all the effort it takes to get that chest opened (even without your teleporter issue), the loot it contains is kind of crappy.
You can drop the other teleporter stone in the battlefield, return to the main game, make a new save, and do some file swapping to get a replacement set of teleporter stones. See the topic Inventory files
(there is one set of stones for act 2, and a different set for act 3).
If you have a problem with the download files from the English version of the game, you can use the inventory files from a previous save. If you don't have any saves with both teleporter stones, you can start a new game and skip to the end of act 1.Hex editing - gold, experience, stat/skill pointsActiontrip.com's Beyond Divinity Cheats
- starting a new game with stronger charactersTeleporting anywhere (via hex editor)
Speaking of hex teleporting, you may be able to shift one of your character into the bush close enough to pick up the teleporter stone.