It seems that feu also exists as an adjective meaning "late", i.e. deceased, so the mpl form would then be feus. However, in the more normal use as a noun, meaning "fire" etc.,  the plural is feux.

Ah oui, vous avez bien raison, Alan. Je viens de relire l'entrée sur WR. C'est clair que le forme << feus >> est toujours adjectival. Interesting that inflection for the adjective form varies only when preceded by a possessive determiner or definite article, i.e. (la feue Reine / feu la Reine). Language is just ever so fun. Thanks for the help!