Not all of the Guardians had gone after Xander. There wasn't a direct order from any leaders for them to do this. The guardians acted on their own accord, but they knew of the situation due to a specific power that allowed them to communicate together. With each bit of new information received, they were able to tell the others what was happening, where they were and more.
Some Guardians decided to go after the one who had stolen the crystal, while a few had gathered around the lab where it all began. They didn't need to go inside to understand what was happening, as they could feel the energy shockwaves halfway in the settlement.
Due to this, some of the guardians unanimously decided to stay outside and control the commotion going on. But many Red Vampires wanted to enter the lab to know what was happening. After all, nearly all of the red vampires were combat oriented, they were different compared to the last vampire settlement.
