The weapon the royal guards carry is called a force pike. They are not lightsabers like many people would like to think.
A force pike operates much in the same manner as vibro weapons.
A vibro-ax is a type of bladed weapon that uses a compact ultrasonic generator to create vibrations along the cutting edge's surface. This drastically increases the weapons lethality, allowing it to lacerate with minimal exertion from the wielder. Similar vibration-based technology can be found in vibroblades, bayonets, and force pikes.
One thing that is obvious it that it is used in conjunction with the martial art echani
that the royal guards master.
I imagine that while force pikes are not lightsabers, they are most likely used in much of the same manner. Even more so, I would be willing to bet that they could use force pikes and lightsabers interchangably, both effectively lethal.