"Others warm by the fire at the center of the monastery"

"warm", in that context is being used as a verb, as in "Come inside and warm yourself." or "Let's warm the chicken in the microwave." I actually don't think that's quite what we (the Monastery) intended, but that's how it's being used.

"Warmed" could be a present participle attaching itself to an unspoken but implied "are." Spelled out explicitly, it would be "Others are warmed by the fire at the center of the monastery." Again, I don't think that's quite what we intended.

"Warmed" could also be past participle, as in "Others were warmed..." But I don't think that's what we intended either.

"Warmed" could also be the past tense of "warm" (in some languages it might be considered a past incomplete, in this context). In that sense, "Others warmed by the fire at the center of the Monastery:" (followed by the list) is correct and probably what the text ought to say.

Another correct verbiage would be this:

Others warming by the fire at the center of the Monastery: (followed by the list, of course).

In this case "Others warming..." includes an implicit be-verb which is not spoken, though it could be. Spelling it out fully it would be, "Others who are warming..."

It's been ages since I diagrammed sentences in honors English in high school, so I may be way off, but if I am, just humor me because I'm unlikely to change the way I talk at this point in my life anyway. *grin*