All of the deaf characters are played by deaf actors.
The conflict portrayed over cochlear implants and other advances to help deaf people hear is actually quite accurate. There's a strong controversy in the deaf community over such devices, and a fear that encouraging such devices treats deafness as an illness to be cured rather than just a different way of being. Different people in the deaf community, as well as non-deaf family members and researchers, have taken a variety of views on the matter.