I can't speak to how knights operate in your country, but Armsmen are a Count's private force, whose oath to their lord is seen as sufficient defense against even treason if they were operating under orders. There's a limit of twenty per Count. Historically they've often functioned as a defense against Imperial tyranny when necessary, though fortunately that's not something I've had to contend with.

[ Seeing as he's not a tyrant. ]

In practice they're... effectively members of the family. They and their families live with their liege-lord and operate as batmen, bodyguards and attendants.