So you placed both pendants on the pedestals, by interacting with them? They register properly and light up on PC, so there must be an issue specific to PS4.
I'll create a bug report for this. It may help to have a save at this point, and maybe one before doing the twin dungeons, if available. You would need to be transfer save(s) to a USB flash drive first. In the Saved Data in System Storage section of the Settings menu, click Copy to USB Storage Device, select the relevant save(s) and Copy. From there you can optionally zip the saves first, then copy to email (supportdos@larian.com) or upload to Dropbox or Google drive, etc, and provide a link.
