I don't know what to do anymore.

Certain key words in your post catch my attention. One is the word forget. If dad is forgetting things, does that mean that he suffered mental decline and memory loss with his stroke? If that is the case, then dad needs to be cared for, since he may not have the ability to do it himself. If mom is not doing that properly, then I'd have to take care of it. Caring for a person around the clock is a huge job. Maybe, she needs help. Will she accept help?  

When you ask mom to do certain things and she gets angry, is her behavior reasonable? If not, I'd ask why. People who don't take their medications can develop medical and mental problems. I'd insist that she explore why she's not taking care of herself and dad. If she still resist seeing her doctor, taking meds, and it' results in her neglecting dad's needs, then, I'd have to step in.

Are you their POA? I'd see an attorney to get legal advice regarding dad's care. Regardless, I would not stand by and let dad suffer from lack of care. I'd let her know that politely, but firmly. I'd be my dad's advocate and make sure he's properly taken care of, whatever it takes, though, I wouldn't relish going to court about it. 

I used to think that my LO was stubborn because she wouldn't use her cane or walker, but, then I discovered that she merely could not remember to use it. That could be the case. If so, then they have to under supervision so that they can be reminded to use their cane or walker.

I might try to spend several days around the clock with them and observe how they are really functioning, so you have an accurate picture of their actual abilities. I don't think that pleading, convincing, threatening will help the matter. Most seniors don't respond to it and if they both have mental decline, they wouldn't respond to it either.

I hope you can get some answers and that something works.

I think let them do what they want to. At this age, it is very difficult to make them understand. So just let them do what they want. Trust the almighty.

I think your mother is worried loosing your dad, it is a difficult time. Allow her to do things for him and just tell her to take care of herself too, what she does further is up to her. Just be positive GOD is great, stop worrying and make as if you support and understand your mother in her presence in that way it might get through . It is not an easy time and all of us will go through the end times with our families. GOD bless

Mom is burned out from caring for Dad. On the other hand if the MD finds something wrong with her, she fears for who will take care of him. You are in the watchful phase, afraid something bad will happen. Try not to smother them with your concern, they see it as nagging.