Going back to what I said in the last chapter, I don't think that Sides can enter other Side's rooms without trust. Here's my reasoning for it.

 Virgil never gave any of the Sides permission to go into his room because he didn't trust any of them. But, in 'Accepting Anxiety' they got to go into his room with Thomas because I think he trusted Thomas to some extent. I think that all the Sides trust Thomas so if Thomas goes to another Side's room, all the Sides are going as well seeing as they are part of him. With 'Moving on Part 1&2' Patton trusted all of the other Sides, so naturally, they got to go to his room. Now, Janus is a little more difficult. No one trusts Janus. I don't even think Thomas trusts him. He's only just been accepted. ANYWAY, I think that the Sides trusted Janus in the past and that's been enough for him to be able to go into their rooms. For example, in (I think it was) 'Embarassing Phases', Janus pops up in Virgil's room but Virgil obviously doesn't trust and actually despises Janus. Why does he hate him so much? I think it's because Janus had Virgil's trust once and somehow betrayed him. Not sure how, but he did. Somehow. And that's when and why Virgil left the 'Dark Sides'. But Virgil trusted Janus once, therefore, Janus can now come into Virgil's room whenever the Hell he wants and Virgil can't stop him. Also, I think this is where Janus gets the clothes that he impersonaites the other Sides from (did that sentence make sense?). In SvS, Janus popped up as Logan but he was wearing Logan's old tie. Logan, obviously, was wearing the right tie but if Janus could materialize clothing out of thin air to impersonaite the other Sides in, why did he get the tie wrong? I think it's because he sneaked into Logan's room to get the clothes he needed for pretending to be Logan and that was the only tie left. I think that all the Sides trusted Janus once and he betrayed them somehow.

Yeah, it's a little odd but I'm ill so cut me some slack. Anyway, please tell me what you thought of my theory in the comments.
Bye,
Queenie