Does anyone know anything about them? Are Falmer intelligent enough to take prisoners and enslave them and if they are how did they communicate that to their captives? It just doesn't make sense.

I would imagine the answer to both your questions would be "Yes."

Yes they are intelligent enough, and yes they give them orders. I would imagine they do this through spoken language. They're blind, not deaf or mute. The servants are probably survivors of Falmer raids that the Falmer found useful in some way. Perhaps they carry out espionage or other activities that require talents the Falmer lack, such as blending into society or the ability to see.

They were probably babies or young children when originally captured. Easy to mold into a loyal servant.