The fallen king
After the incident with those that called themselves the true form vampires, the Tenth family was in recovery mode. Now standing outside the inner castle, were a few vampires from the royal family who were each as strong as a vampire knight.
They were placed there just in case anything else was to occur. They had realised after the attack that the Tenth family were the only family who were attacked. None of the other vampire families, or areas had been touched.
Even though the supposed leader of the true vampires were dead, they still suspected that there were more blood suckers out there that hadn't joined in with the battle, without a leader, or perhaps now under the control of whoever was helping them before, which was why the guards were placed there.