I breed Peis, and rarely have problems with mine.
Peis were used for fighting, but they were bred for other purposes. Namely, hunting and guarding, but they were also used for herding in some areas.
my advice with Peis is socialization and training. your aunt just has undersocialized dogs that needed to be trained better as younger dogs. that is, assuming there is nothing mentally wrong with the dogs, which i highly doubt.