Five witches besides Isabella ward the colony site. Robots guard the site of the portal, obligingly letting colonists through during scheduled trips and reporting to Isabella by mirror if anybody else shows up. Other robots help the colonists with setting up their farms and houses in the warded area. It'll hold a city, no problem, although another transfer of silks and bags to pay for warding a second site is going to be called for before they get literally everyone across, since in addition to city they need farmland, and since they can't build vertically as effectively as fully industrialized Earthlings or the deceased aliens.
One day:
"It's been exactly a year now since you crashed my picnic. Let's go to a fancy restaurant and celebrate."
From the look he's giving them, they can probably figure out that he will not be pleased with them if they kill the masquerade before he's ready.
"I see. It's probably not worth the trouble, but that also depends on the time frame. How long are you expecting to need to get into a position to safely drop the pretenses?"
"Possibly less than another year, probably fewer than three. If something let it slip right now I imagine we could deal, but it would be irritating and we'd prefer controlled press release to accidental leak."
She snorts. "Less than three years? That's simple, I was expecting to wait for a few decades, at least. Even if it took you five I can stay hidden without any issue. Not worth the trouble of pretending to be something I am not for such a short period of time."
"Where are you planning to hide? Loosely speaking in terms of parameters, I don't expect you to have an address picked out."
"Some place reasonably far away from any who would disturb me. I don't speak the language, but it's easy enough to just avoid people for a few years and get by with aid of the ghosts and my own skill."
"Whatever they want to? Most will remain with me, but a few will be curious and explore."
"Nobody but you lot can see them. Are they good about staying out of private residences and not eavesdropping on personal conversations?"
"I doubt doing so will interest any of them," she shrugs. "They gravitated to me because I return conversation. Not many people talk to ghosts, but they can spy on whomever they like. In a way, it has been cleansed from their system."
"...Okay. If they create problems the fact that we're the only people who consider 'ghosts' a possible class of problem-causing means I will consider it my business, but I suppose I have no overwhelming reason to be more suspicious of your ghosts than I am of anybody else."
"How do you feel about passing for a witch to casual inspection and being generally available to make yourself useful around our projects as first aid or anything better we come up with?" asks Isabella of the one with the bird. "Passing implies a wardrobe change but not necessarily much else if you don't want to talk to people a lot."
"I'm... Not sure where I'll go or what I'll do, now that I'm here. Those work, as well as anything else. I'm fine with passing for a witch, and being available to be - useful to projects."
"Okay. We can put you in a hotel near a portal location for the time being, maybe outfit one of the bits of the hub building as a live-in office for you after that, I don't think I want a houseguest."
She remembers what she and her companion interrupted, and looks suitably embarrassed. "No, I expect you won't. Thank you, that's very kind."
"Mm-hm. We are currently in the city of Chicago, for reference." English. "Adarin, how do you feel about language-ing her, I can just write her one of those how-to-hotel phrasebooks if you have misgivings...?"
He goes and finds his book of cheat-sheets, finds the appropriate page, and does the spell.
"Okay. Even being able to pick up English, you're probably in for a bit of culture shock, we could maybe leave you a mirror. What are your names?"