The Old Spanish change homne > homre is dissimilation. When two nasal consonants came together the second lost its nasality. The next stage is epenthesis of a homorganic stop, as a strengthening of the abrupt transition from one place of articulation (bilabial /m/) to another (apical /r/). Interestingly the whole sequence of changes is paralleled:

homine > homne > homre > hombre (and losing the /h/ somewhere in there, probably at the omine stage but I won't swear to it)

cheminée > chemney (> chimney) > chimley > chimbley

The word 'chemination' looks badly formed. The Latin was caminus, Greek kaminos 'furnace'. I don't know how the sense of 'way, road' arose (camino, chemin). So the Latin should give 'camination', and the French should give perhaps cheminage.

I suspect 'chemination' might be a made-up word by someone who wasn't too fussy about mixing languages. Perhaps they had in mind an admixture of 'chemistry' (which is of course unrelated).