I have second-hand knowledge my 82-year-old relative is being emotionally (and once physically) abused by his younger wife. What can I do?

Lynn, my apologies.   I assumed "access" to a gun meant there was one in the house.   Sorry about that.

Maybe not APS maybe Office of Aging to start. Ask if there are resources to help this woman in her area. Maybe Medicaid homecare if their income is low. In my opinion, if she talks to people about what she does, then she feels guilty. She may have no idea why she gets this way.

Horrible. But, as already said, she is probably burnt out. He would be much better off in a nursing home. Perhaps he it is even time to consider a hospice evaluation (depending on severity of kidney failure). What a sad way for his life to end.

Lynn, if the wife herself is sharing information with you about her difficulty in caring for her husband, I'd consider that a potential cry for help, or at least expressing her frustration.   Given depression, she's probably literally "at the end of her rope."

I'm assuming there's NO help in the home at all?   Or that none of the family have raised the issue of getting help for both of them?  Including the daughter and younger sister?   Would they help if they had guidance and were asked, or are they nonparticipatory?

Before calling anyone, I'd spend some quiet time with her, perhaps at a luncheon or someplace away from home, and try to sort out where she could use help, i.e., with home chores, with care for her husband, etc.   Try to work out a care plan; if you need help or guidelines, just say so.  Others here have gone through similar challenges. 

And ask what she feels are the most challenging roles, i.e., caring for her husband, medical trips and appointments, house maintenance, etc.   Divide them in categories, and ask where she thinks she could use help.     Sometimes just hiring Molly Maid or a similar company can help alleviate the burden of housework.

And a doctor prescribed home aide can help him with personal care.

Are you familiar with any home care agencies and their roles?   With home PT or OT? 

Is he being treated for kidney failure, or is it at a terminal stage?  (I'm not that familiar with kidney failure and its treatment so my question may not be appropriately asked.)   Is he getting any home care through the doctor who's treating him for that?

I would also contact law enforcement and ask how to safely remove the gun.    In fact, I'd do that first before anything else.   You might also raise the issue of concern, i.e., that both need help, and ask for their suggestions.  Some police are better at handling these issues than others, so that would have to be  your guide. 

I would also emphasize that the family's trying to work this out amongst themselves before considering intervention.   You won't want the family torn apart.

And I think if there's any consideration of the daughter and younger sister becoming involved, now is the time for them to do that, even it if it's just in planning.

Does the wife have help caring for her husband? Younger or not, taking care of of someone in your relative’s condition is hard work. It’s not easy at all. She sounds burnt out and if family is aware and not willing to help out, the least they can is call APS to get the ball rolling so these people can get some help

How reliable is this second hand knowledge, and why isn't that person taking action?

Have YOU ever witnessed any of the issues of which you write?  If not, tread carefully and don't make accusations you can't support. 

Why are the daughter and younger sister not taking action?    Think about that seriously before you step into this situation.

Call adult protective services and tell them what you have told us. Call them today.