To me, two of those gravestones look a little like pillars (Mainly, the ones to the right of the image with the small black parts on them). Look to the top of them, they look a little strange to be gravestones. Is there any moving footage of them? That'd probably help discern their identity a little.
If it turns out that they are indeed graves, perhaps they are placed whenever Kamui defeats a sibling of the opposing nation. I think it'd be better than killing them mercilessly, or sparing them. It would still leave a slight feeling of guilt, though the dead have moved on, so it's slightly reassuring, I suppose. Plus, people seem to love the siblings from both nations, it'd be weird to do nothing special if/when we kill them.