Yes, as a landowner, you have the option to allow additional factions to settle in your county. By default, only players of the county's faction can settle on your county. However, county owners can choose to permit players from other factions.

If a player changes factions while settled on a county that does not allow their new faction, they will be automatically evicted. Additionally, if a landlord decided to remove allowance for a faction to settle on their county, all players of this faction will be evicted. It is not possible to remove allowance of the counties faction.