I think bartuc’s head is held at the Tibault statue.
If you look closely there is a golden Zakarum and Rathma marker right next to it. Those are the two parties who hid his head and body right?
When you get close to tibault statue the game literally zooms out. It’s one of the only places that does that.
Still not sure about the second tomb. But interestingly Symon requested to stop at the tibault statue on the way to his demise.
The head of the tibault statue has been vandalized and removed and is lying on the ground next to it.