i'm not allowed to use Murk port and evac, since someone in the group hadn't done Murk faction. Is this correct?
Yes, that is correct.
This would be an exploit to circumvent the aggro from the guards standing right there.
Not to rain in your parade Tarutao, but wouldn't it be much easier to just increase the aggro range of the guards a tad and/or make them actually face the portin, instead of making such a hard-to police rule?