From Denial to Recognition
One thing you don’t want to do might be your first impulse – to act as "their ears." Don’t repeat yourself, raise your voice, or act as a messenger. This will only allow them to either stay in denial or to simply continue living their lives with poor hearing. You're only enabling them to go without the help they really need.
It's also very important to get as much of your family and/or friends involved. A group effort in convincing a loved one to resolve their hearing issue is a “strength in numbers” approach that will give your point more impact and urgency.
Both of these approaches will help them understand that their hearing loss is negatively affecting more than just themselves, and that a solution must be considered.