"Loch Ness?"
To be honest, if not for being siblings since childhood, the three sacred beasts in Ainsley's family would not be able to get along 'harmoniously'.
And as for the territorial instinct, they had the magical prairie as their territory and to be honest, the three beasts also included the Sloan Family's whole territory as their own.
This was also why they became guardian beasts because once they included something into their territory, they would work hard to protect anything inside their territory.
The so-called guardian beasts of many forces were just to make the sacred beasts feel a sense of belonging to their family and thus, including that family into their circle of territory.
"There's no way a monster with a strength equal to a sacred beast won't be sensitive to things related to their territory."