I agree with Sqad. Mum and I both have Menieres Diease and she is quite significantly hearing impaired now, with the additional complications of pressure and tinnitus which increase the issues she has hearing. Headphones have helped a bit, but only for very short periods when she can tolerate them and only really when there is a clear conversation. It's easier one to one, if there are family chats, especially with children/background noise, then maybe make sure there is time for some one on one time somewhere quiet as well. As said above the chat function can be useful.
I adjust myself to her as much as I can, make sure that the room is quiet, so there is no background noise interfering and speak as slowly and clearly as possible (but in a normal way, not saying anyone here is but some people can tend to go a bit OTT, like you're a young child or stupid or speak in a more "shouty" manner). I also look for cues that she might not have picked up what is being said, especially when it's a group chat, so she doesn't feel left out and to cue others to repeat things etc...
Lipreading is a skill in itself, but just generally have them clearly face the camera so that it's an extra help, and sometimes general gestures and facial expressions can be an additional assists. Many years back, I found when I was learning some basic sign language, even though I was only a beginner, when communicating with people with hearing issues, I found that I could communicate a bit more than just with actual official sign language. It's something that can be developed over time, but that can be easier if they are communicating with the same person.
Do you have a local deaf centre? The one near here is brilliant. They may have ideas for things that could help and get togethers where he could meet others with hearing issues in a supportive environment, likely pick up some good ideas from others too, and maybe where they could too.