What can she do?

Lookingin, I'm so sorry, but no one is safe from GG now, not even Poppop. She has threatened another human being with a knife, and you can't trust her not to do that or some similarly aggressive act again. Dementia is a terrible disease, and GG as you knew her is GoneGone. She didn't recognize MIL, and the next person she doesn't recognize could be Poppop or the neighbor or the mailman. What if she attacks them? It must be awful to be GG now because she is so frightened. The first thing that needs to be done is realize all of the above and secure GG in a place where she can't hurt herself or anyone else. At that place, she will get medicine to help her with her emotional control, agitation, and fear.

As for Poppop, he's sick too. No person who is in his right mind would be thinking as he does. Furthermore, if GG has been seeing her PCP regularly and is in this state of dementia, there isn't any way that the doctor wouldn't pick up on her cognitive decline. Doctors who do Medicare wellness yearly visits are required to do a cognitive assessment every year. So Poppop may not being telling the truth, may not have been told the truth in the first place, or he may have forgotten it because of his own dementia. Or maybe it's just a bad doctor.

Someone with half a grain of sense must call the grandparents' PCP and tell them what's going on. Ask to talk to their doctor's nurse. Or you can write a letter to the doctor and say that they need help immediately. Then do what they say.

ByeBye and LuckLuck.

You are three steps down the ladder from having any real say in this. Your grandfather is making the decisions, their daughter your MIL can’t or won’t change things, your husband can’t or won’t step in forcefully. You are the spare wheel. The only thing you could do is to report the situation to the appropriate authorities for a check, with prior information – particularly that grandfather will say everything is fine.

Being hurt, while certainly understandable, helps nothing. Anyone in the family can inform grandma’s doctor of her mental status, and should do so. HIPPA laws prevent the doctor from talking to you, but not from listening to your concerns. Put it in writing and see that her doctor gets it. And your MIL really should back off from providing any help at all. That may sound heartless, but her father will never see the need for help as long as she’s trying to be all the help. Leave him to it, on his own, and he should see soon enough that he can’t do it all on his own. He’s taking an enormous and foolish chance with his own life, I’m sorry he’s too stubborn or prideful to see that. If and when he wises up, be ready with realistic options for help. I’m sorry your family is going through this

The second the knife-pulling happened the police should have been called at once. G.G. needs to be placed before MIL commits a homicide in self-defense.
One of you needs to contact APS (Adult Protective Services) and tell them exactly what's going on with PopPop and the demented grandmother-in-law.
Then the MIL needs to go to the police department in their town and ask the cops to start doing regular wellness checks on them because there is a near invalid man trying to care for a violent maniac with advanced dementia. The cops will go there.
Then all you can do is wait for the other shoe to drop. Hopefully it won't be in the form of a serious crisis or injury.

Nobody is fine here, and all these cutesy names are driving me to distraction! Your MIL needs to leave her folks alone & stop enabling them to pretend they're 'independent'. Once a crisis happens, which it will, THEN her father's decision making ability will be removed, and the two of them WILL be placed in managed care where his wife will no longer be able to pull a knife on her daughter that she no longer recognizes due to dementia.

Calling APS IS an act of love by your MIL; it can wind up saving her mother's LIFE, since her DH isn't addressing her needs properly.

Your MIL needs to stop feeling 'hurt' and realize what dementia looks and acts like. It's probable they're BOTH suffering from dementia, just varying degrees of it, the mother much more so than the father, who cannot properly care for his wife but is too stubborn to see that AL is necessary now. Your DH needs to stop 'giving up' and belly up to the bar to understand what's going on here so he can support his mother who's feeling 'heartbroken & defeated'. Him burying his head in the sand isn't helping anyone with anything.

Everybody in this family needs to understand & learn about dementia and how it presents itself. Being that "GG is lucid again" just means that she's having a good day. When she pulled a knife out, she was having an extraordinarily BAD day. Ups & downs go with the dementia territory, although when a knife comes out, it's time to be placed in managed care before someone DIES as a result of the bad day GG is having. Not to mention, she should never be left alone with THIS level of dementia at play, it's not safe. Whether her DH wants in home help or not, it's necessary now.

I suggest you & everyone in your family read this 33 page booklet which has the best information ever about managing dementia and what to expect with an elder who's been diagnosed with it.

Understanding the Dementia Experience, by Jennifer Ghent-Fuller 
https://www.smashwords.com/books/view/210580

Jennifer is a nurse who worked for many years as an educator and counsellor for people with dementia and their families, as well as others in caring roles. She addresses the emotional and grief issues in the contexts in which they arise for families living with dementia. The reviews for her books are phenomenal b/c they are written in plain English & very easy to read/understand. Her writings have been VERY helpful for me.

The full copy of her book is available here:
https://www.amazon.com/Thoughtful-Dementia-Care-Understanding-Experience/dp/B09WN439CC/ref=sr_1_2?crid=2E7WWE9X5UFXR&keywords=jennifer+ghent+fuller+books&qid=1657468364&sprefix=jennifer+ghent%2Caps%2C631&sr=8-2

Here is a list of useful tips from her e-book I found to be excellent:

The “Dont's”
· Do not reason and argue
· Do not demand that they reason or problem-solve
· Do not demand that they remember
· Do not demand that they get their facts straight
· Do not correct their ideas or scold them
· Do not reorient them
· Do not think that they are being uncooperative on purpose
· Do not think that they really do remember, but are pretending not to
· Do not use a “bossy” dictatorial attitude in care
· Do not act with impatience

The Do's
· Enter into their frame of reality, or their 'world'
· Be aware of their mood or state of mind
· Use few words and simple phrases
· OR use no words, just friendly gestures and simple motions
· Do everything slowly
· Approach from the front
· Wait for a slow response
· Constantly reassure them that everything is 'OK'
· Keep people with dementia comfortable 'in the moment' - every moment
· Maximize use of remaining abilities
· Limit TV or radio programs which they may feel are frighteningly real
· Maintain privacy
· Provide a safe physical environment

Wishing you the best of luck dealing with the reality of what's going on in your family.

"My MIL lives 1 1/2 hours away from GG and Poppop. Her brother lives 15 mins.
She drives there every weekend to to shopping and cooking for them or take them to doctors appointments."

Please tell us more. If your mil drives there every weekend, how can doctor appointments be included?

"Poppop doesnt want to go into assisted living"

Poppop doesn't get to decide, since lives are being endangered now.

Jenn, you are 30...how is it that you are the one who is looking for solutions? Do you think that your H (who has given up) and you will soon inherit this problem?

This post is a bit confusing. Your profile doesn’t explain the situation clearly either.

Anyway, from what I read, neither GG, nor Poppop should be left alone in their home any longer by themselves.

GG is definitely a danger to herself and others. Poppop has had it! Who knows what this man has endured living in this situation? This is very sad.

Your MIL cannot handle this situation anymore. It’s way past family members helping out.

GG and Poppop need to be placed in facilities where will receive care from a professional staff.

Wishing you and your family all the best.

What can your MIL do to get more care for her mom? Is that the question?

If your MIL thinks her mother is in harms way she can call APS.
Adult Protective Services and request a wellness check.

How old are the grandparents? Does the GP have dementia as well?
Does your MIL live with them?

Are you saying that while GP was in the hospital, MIL “pulled a knife” on her mother because she was frightened?

Give a bit more info and it will be easier to get advice.