Sure. They could be a Grotesque that is also a Family or a Cult or a Prison or whatever. Here is my top secret technology for building Threats (and Fronts in general): combine threat types, when it makes sense, and then think about what that means.
So while yeah, most Grotesques are single people, maybe some aren't: or on the surface they aren't, but they act in the fiction like a single person, they have some unity about them that makes the Grotesque type and impulse and moves make sense. What happens when a Family of Cannibals 'tells stories' or 'demands participation'? What happens when a Landscape/Prison that is also a Warlord/Slaver 'makes a show of discipline'? Etc.
Here's two Grotesque threats I made, for the same game (it was a cold apocalypse, with frequent snow, and the snow was not safe to eat/drink.) It was awhile ago so bear with me.
First there was Parcher (irony alert), a Grotesque/Disease Vector. Parcher worshipped "the static", the strange and endless interference pattern that had its claws deep into the world (he was part of a larger Front of that same name.) He was not a Cult, since he worked alone, but he shared the Cultish impulse to "victimize and incorporate people" -- the thing he wanted to bring them into was the static, his disease. And the way he did this was through the snow, the physical manifestation of the static in the world (and itself another Threat under the same Front.)
Parcher's method was straightforward: he would befriend people (especially desperate people), or otherwise lure them to his home, and then offer them water (as any generous host would!) The water was of course melted snow, but he was pretty good at seeming harmless; and his friendliness was genuine, if horribly misguided. I imagined him as a kind of slightly addled Jehovah's Witness; since he himself drank the snow-water, his behaviour was erratic and he was prone to lapses of memory and identity. And of course, when just being friendly didn't work, or if his guests refused his offer, he would often resort to violence. His home was beneath an old school, and he had several lockable rooms: if he was able to overwhelm his guest, they would find themselves locked up underground, and the only thing they had to drink was... well, you know.
In our campaign, Parcher hit the jackpot when certain actions of a certain Maestro D' resulted in the neighbourhood's only working water filtration system exploding into a pile of useless parts; the PCs discovered him at the local market, selling his 'hoarded' supply of 'fresh' water to desperate NPCs, friendly as all get out. Eventually this all resulted in a somewhat misguided raid on his home, culminating in the Battlebabe (and Maestro D', I think) locked up inside. Eventually they were 'rescued' by a very grumpy Savvyhead, and Parcher went under the crosshairs.
--
The second Grotesque was a bit more complicated to figure out. He appeared in the very first session, and his name was Abs, and he was trying to sell the Savvyhead what were incredibly-obviously stolen goods. Abs was all glib and transparent bravado, first overheard in the hallway outside the Savvyhead's place giving himself a pep talk before trying to close the deal. Abs was not harmless -- his incompetence, desperate friendliness, and constant hustling was a threat to everybody -- but he sure didn't seem that Grotesque. In fact (and I may just be projecting here) everybody loved Abs -- or at least they must have loved him at least a little bit, because they at least occasionally made efforts to stop him from getting himself killed.
When I introduced Abs, I was not thinking about him as a threat, I was thinking about him as an NPC with a face and a name and a desire to make a deal at all costs, including his own ability to continue making deals thereafter. It wasn't clear what part of himself he was following around, but he was definitely following something, and following it real hard. Abs was nothing if not persistent.
But Abs was clearly a threat of some kind. He had to be -- he wasn't a PC, so he was a threat. And since there was only one Abs, and he clearly did not have any friends (the very next thing we learned about Abs after the stolen goods was that he was banned from the Maestro D's establishment), he had to be a Grotesque of some kind. He just wasn't complicated enough to be a Landscape in disguise, and while an argument could be made (by, say, all my players) that Abs was clearly an Affliction, the Affliction moves did not really fit, whereas the Grotesque moves were perfect.
Since Abs was in the Home Front I had some time to think about what exact kind of Grotesque he might be -- unlike other NPCs, where I often used their position as a Threat to help get a better handle on their characterization, I had no trouble playing Abs or figuring out what Abs wanted or was like, so I let Abs' threat-ness slide for quite awhile.
Eventually though, probably like six or seven sessions into the game, I figured it out. Abs was also a Disease Vector. He craved contact above all else: contact with other people, who would be his friend or help him make this deal or loan him a jug of water or hey hold this for a second I just need to go over there, no it's cool. And he clearly wanted the contact to be more intimate than anyone else was really interested in (the Maestro D' ran a brothel-esque establishment, and Abs had been kicked out due to over-eager pursuit of an uninterested employee.)
So the impulse fit perfectly, but the name was kind of weird. Abs didn't seem very sick, and all he really spread to people was a kind of annoyance or malaise at him being around -- though he certainly spread that as enthusiastically as possible. So what exactly was Abs disease, anyways? Well, it turned out Abs' disease was hope. Hope and optimism -- about his own abilities, about his prospects for the future, and about how other people would treat him. No matter how many times Abs fucked up, or got told off, or got shot, he was not dissuaded. Because he was gagging sick with hope.
This all crystalized for me when, it being my turn to talk at some point in the game, I decided to have Abs 'display the contents of its heart,' as Grotesques do. The PCs were visiting Abs in his new home, on the outskirts of a 'hold (threat type: Brutes/Family) that lived on the shore, and made their living fishing the (highly static-compromised) waters. It was a shitty home, even as the apocalypse goes, and I seem to recall that Abs immediate desire upon being visited was to get help from the PCs in dealing with his unruly landlord, which they did kind of by accident. But in any case, at some point Abs left to do something and naturally the Maestro D decided to snoop through his stuff, prompting me to reach for the move. The Maestro discovered a metal box containing a cache of polaroid photographs that Abs had taken -- as well as the camera he took them with. All the photos were of the city in which the PCs lived, of various buildings or locations -- and they were all marked up with notes. Notes about how to transform them into something useful, like a park or a school or an aqueduct system. And there were notebooks too, full of plans! Plans to fix everything, and make the whole neighbourhood into a wonderful, healthy, friendly place to live.
And none of these plans had the slightest fucking chance of ever coming to pass. Because Abs was not a PC, he was a threat. He threatened the notion that what everybody already had, what they were barely scraping together, was actually enough.