I would propose an alliance system. Have a rating for every other faction
in relation to yourself. ie Friendly, neutral, unfriendly, hatred.
Friendly: You are openly friendly towards the faction/character. They may
enter your structures freely (paying appropriate fees of course).
Neutral: Default. The person has been untested as to his loyalty. The
faction/noble is barred entrance to your structures.
Hatred: You really hate this group. In fact you may even attack them on
sight. Be careful who you hate and where as you may attack them
when you really don't want to.
This system will also clear up some of the attack/movement problems allowing
for other possibilities.
Allan