They've been married for a long time, and it's good to know that nobody has mentioned physical abuse with your aunt, but there may have been occasions that nobody is aware of. There are a lot of marriages unfortunately, where the good moments may be more than the bad, or the wife is very much in love and will tolerate verbal abuse for the duration of the marriage. This sounds like one of those cases.
If you aunt is still independent, functioning on her own, paying bills, shopping and completing tasks around the house, goes to the doctor when needed, etc., maybe she should be left to handle her own private life. It's still a good idea to be there for her if she ever does want to share, but it's not likely if her husband has a short fuse.
If she wasn't mentally alert and able to care for herself and her responsibilities, I might feel differently. But I know, if I were in her shoes, even if I was sad and crying sometimes, I'd prefer to be left alone and given my privacy. I'd be furious if someone called the police to come and visit also. If I just had an argument with my husband, and someone visited unannounced wanting to come in, I'd want them to respect my wishes of not entering my house.
If she had bruises or wounds, it would be a different story. Just my opinion from everything you've said about her.
