When, how and why to buy hearing aids?

Question
Siblings Chuck & Sherry say:

Communication is starting to get pretty dicey at my parents home.  Their not hearing us or each other used to be funny and cute but that has gotten old. What also is annoying is the straight out denial.

Both my mother and father are losing their hearing and we used to have fun teasing them but now it is a sore subject and we dare not mention it. Someone has to make the next move! The silly stupid arguments I hear them getting into are because of one of them misunderstanding something and then they get into it and star blaming each other. 
The extremely high price they are paying to keep their hearing loss.

How can I help them?

I know they love each other and they deserve every happiness. But life is short and goes by quickly!  Seeing my dad shutting down and avoiding family parties and other social situations, and resigning himself as a non participator, hiding behind a book, is very disheartening.  I hate to see them in conflict and I don't even think they understand what is happening to them.  Please help!