I take two things away from that part about the deaf employees being frustrated.. a) their speech isn't clear enough or b)they use ASL exclusively but hearing employee isn't skilled enough yet to understand the ASL.
I'm kind of betting on b). Definitely would do some sort of sit down meeting- involve the higher up (if there are any managers/supervisors above you 3) or Human Resources even to try to work out a solution.
Or.. text each other in the same room. I know that's a 'negative' side of technology as bleated by so many people but that actually works for a friend of mine and me when I visit her. She's hearing but hates social interactions about as much as I do so we sometimes text each other when there's a whole mob of people (that happened- she broke her ankle, had to be on bed rest generally so people gravitated to her room- drove her nuts).
