I was thinkning you can move the portals to the other side of the wall in the same building they are already in so they have one space in between them. In that space you could put different NPCs saying "Use this portal to go to _________". So the new players don't have to keep asking others which portal is which.
Here is something I did in paint to sort of draw it out:
Maybe you could think about this. It also gives a lot more room too =)