"It's not surprising you've heard of them, we're all old acquaintances. The Koslow family's ancestors also originated from the Northern Border, and they are a rather capable intermediate aristocracy.
Only, they chose the wrong side back in the day, refusing to accept the goodwill of the Rocknard family. During an Orc invasion, they lost their ancestral lands, resulting in the downfall of their family estate.
The current Koslow family in the Kingdom was established by the remnants of their surviving members scattered outside, whose most notable trait is their thriving population.
Possibly fearing continuous pressure from the Rocknard family, they changed their strategy from concentrating their family in one place to expanding their family branches after losing their ancestral lands.
Their branches can be seen in many parts of the Kingdom, and some even say that some branches have made their way to other countries.