Cassandra: Initially, she got frustrated upon first meeting the Herald when they kept asking her to repeat herself. When she figures out they’re partially deaf, then she feels a little bad for being impatient with them, doubly so when she discovers they’re innocent of the Conclave’s explosion and the Divine’s death. She tries her best to accommodate them, be it writing down orders or things or speaking louder or repeating herself if need be, and learns later on how to use sign language.
Blackwall: He finds out second-hand, and he’s not really sure how to handle it, so he just copies what Cassandra does. He asks about their hearing, if it doesn’t bother them, and tries his best to learn sign language. He’s a little sloppy at first, but he’s trying.
Iron Bull: Figures it out almost immediately by observing them. He quickly adapts to their needs, and is remarkably responsive and understanding. (Assuming Thedas has some form of sign language) he surprises them by knowing sign language, and it becomes their primary means of communication. He also offers to teach some of the others who want to learn, and eventually most of the other companions can use sign language enough to communicate with the Herald outside of speaking very loudly and writing.
Sera: She’s befuddled when they ask her a few times to repeat herself when they first meet. Her eyes widen when Cassandra explains their hearing difficulties. “Ooooh. You’re deaf, or close to being deaf? Shite, why didn’t you just say so?” She takes to having a notebook to doodle and write in to convey to the Herald what she’s thinking, though often dirty doodles and snark line the pages. She has no problem working with the Herald’s disability.
Varric: While he’s learning to use sign language, he happily communicates with the Herald by writing, a lot, and doesn’t mind at all. In fact, he loves it, and considers it good practice for writing. He picks up sign language quickly and notes that now he can tell a story in person without actually making a single sound. “Now I can accommodate all audiences.” he says cheerfully.
Cole: He knows just how to communicate with them, and surprising the others, he seems to know how to use sign language instantly. He doesn’t use spoken words at all with the Herald, instead opting for signing. “Sometimes ears don’t work, but hands do.” he just says when asked about it. “Hands can do all the talking they need; hands are just as talkative as a mouth is.”
Dorian: He’s a bit surprised, but he does his best to accommodate him. He insists on learning sign language as quickly as possible, and learn quickly he does. “It’s too bad you’re hard of hearing,” he signs to them one day, “because you would LOVE my lustrous voice! I suppose my beautiful hands and looks alone will have to do.” To which the Herald rolls theirs eyes but smiles all the while.
Solas: Starts signing to them immediately; he hardly reacts at all otherwise. It’s no different to him than speaking any other language than Elven. He never explains how or where he learned sign language, and begins teaching the others how to use it. In the Fade, he introduces them to spirits who happily sign to them, if they do not regain any hearing in the Fade. “Spirits will adapt and learn to speak as we speak,” he signs, “and they will accommodate you easily.”
Vivienne: When she sees the Herald for the first time, they’re being harassed by that Marquis, who starts yelling at them for asking him to repeat himself. She scowls as the Marquis begins to mock them for their poor hearing, and she steps in to put him in his place. He’s shamed and humiliated even further as she berates him for being so rude to someone who’s simply hard of hearing. She doesn’t mind using writing to communicate instead, and also opts to learn sign language like many of the others. Soon, she and the Herald sit and look over Skyhold, chatting away about sundry topics with hands alone and some tea.
Josephine: She finds out from Leliana. This is no problem for Josephine, because she learned sign language to better communicate with the various guests that would come to the Antivan embassy. She has runners that know sign language work with the Herald, and makes sure they’re comfortable and clearly able to understand them and work with them.
Leliana: She responds by asking Josephine to teach her sign language ASAP. In the meanwhile, she just writes down what she wants them to know, and doesn’t seem affected by it at all. She does ask Dagna later on if there could be any sort of hearing aid she could give the Inquisitor, but nevertheless is very understanding about it.
Cullen: Similarly, he wants to learn sign language from Josephine or Solas or even Bull. He tries to be polite about it and accommodate them as best he can, but as it turns out, he likes writing down his thoughts and important points down more than speaking anyways.