I'd rather have the player want to place his retainer in all 3 cities on his own accord because it's the best way to do it, rather than have to be forced to do it. Forcing the player to put one retainer in each city doesn't solve the fundamental issue of why the player doesn't want to do that in the first place.

It would be easier to just unify the wards and make it so that the market ward entrance in each city leads to the same instance.