I want to give the royal family a surname in the novel, so I get good points.

There are many royal compound surnames in the novels, and I prefer them:

Xuanyuan, Dugu, Sima, Nangong, Beiming, Huangfu, Nalan, Helian, Murong and Hangong

If LZ doesn't like compound surnames very much, you can also use single words. I think the surnames are

Yun, Mo, Jun, Xiao and Mu.