The original sentence comes from Vergilius:

Carmina vel caelo possunt deducere lunam (Eclogae 8.69)

'Poems can lead even the moon down from the sky'.

In this original sentence carmina is the plural nominative subject of possunt. Note also that the direct object is lunam (acc. sg. 'the moon'), not "luman" (?) nor lumen ('light'). Caelo/coelo can be naturally interpreted as an ablative of separation.

In your sentence it seems that carminibus is a plural instrumental ablative ('with their songs/poems') and the subject is elliptical ('they', e.g., some sublunary spirits? ).

The original sentence comes from Vergilius:

Carmina vel caelo possunt deducere lunam   (Eclogae 8.69)

'Poems can lead even the moon down from the sky'.

In this original sentence carmina is the plural nominative subject of possunt. Note also that the direct object of deducere is lunam (acc. sg. 'the moon'), not "luman" (?) nor lumen ('light'). Caelo can be naturally interpreted as an ablative of separation.

As for your slightly different sentence, the one your wife encountered, I assume, perhaps incorrectly, that the "piece of fiction" referred to in the first line of your question is "The stolen child" by Keith Donohue (published in 2006). Here is the relevant fragment from chapter 1:

"There exist in this world a range of sublunary spirits that carminibus coelo possunt deducere lunam, and they have been divided since ancient times into six kinds: fiery, aerial, terrestrial, watery, subterranean, and the whole class of fairies and nymphs".

In this new (con)text, carminibus is a plural instrumental ablative ('with their songs') and the subject is some "sublunary spirits" that "can lead the moon down from the sky with their songs". As noted, in both sentences, Virgil's original one and Donohue's revised one, the noun caelo/coelo (the latter form being more typical of Medieval Latin/Neo-Latin) is naturally understood as an ablative of separation.

The original sentence comes from Vergilius (Eclogae 8.69):

Carmina vel caelo possunt deducere lunam 'Poems can lead even the moon down from the sky'.

In this original sentence carmina is the plural nominative subject of possunt. Note also that it is lunam (acc. sg. 'the moon'), not "luman" (?) nor lumen ('light'). Caelo/coelo can be naturally interpreted as an ablative of separation.

In your sentence it seems that carminibus is a plural instrumental ablative ('with their songs/poems') and the subject is elliptical ('they', e.g., some sublunary spirits?).

The original sentence comes from Vergilius:

Carmina vel caelo possunt deducere lunam (Eclogae 8.69)

'Poems can lead even the moon down from the sky'.

In this original sentence carmina is the plural nominative subject of possunt. Note also that the direct object is lunam (acc. sg. 'the moon'), not "luman" (?) nor lumen ('light'). Caelo/coelo can be naturally interpreted as an ablative of separation.

In your sentence it seems that carminibus is a plural instrumental ablative ('with their songs/poems') and the subject is elliptical ('they', e.g., some sublunary spirits?  ).