Hello ClairBats
Steve2 is quite right in that your parents are lucky to have two such caring daughters but you are facing, as you know, a very delicate not to say difficult situation - to which if I am honest, there is no easy answer.
The first thing that occurred to me on reading your post was the reaction of your Dad saying your Mum is giving up or won’t try. That me be because he doesn’t know that her Parkinson’s will progress or perhaps more likely that he doesn’t really know or understand what that may mean and so can’t see that your Mum is not being deliberately obstructive rather than she can no longer do what she used to be able to do. It might also be that he does know that and his reaction in saying his wife has given up etc is because he is plain scared of what the future may hold; that may be a fear of what your Mum is potentially facing or perhaps a fear that he himself won’t cope with whatever is going to happen.
It may help if they had some time apart, I’m guessing they have no support that your Dad does it all, although of course that may not be right, but for now I will assume they have no outside help. Do you think they would be agreeable to an assessment by Adult Care Services (a referral can be made through their local council). They may suggest, for example, some home care to relieve your Dad os some of the routine things such as having to help her wash and dress, or perhaps your Mum could go to a day centre - that would give your Mum and Dad a bit of time apart; your Mum will be out of the house and mixing with other people with things to do and your Dad can have the day to himself. They can also, as Steve2 has intimated, have a look at their home and make sure it is set up so they can both manage more easily. Your Dad incidentally, would be eligible for a Carers Assessment in his own right, totally separate from his wife, if he will agree to that.
How you manage this situation is hard to judge, so much depends on the nature of your relationship and how close you are, how much you talk about the future and so on. I appreciate you and your sister don’t want to take sides, but instinct says to me that it is your Dad that needs to accept for whatever reason, things are changing, will change as time goes on and that will be normal for their lives from hereonin. That it won’t be like it was before - suggesting maybe they need some help may give you the opening you need to broaden the conversation but in one way or another I think it is a conversation that needs to be had. Whether that is done with both of them together separately would be something you need to decide. I know not everyone agrees with this but it can work when conversation is hard, there is likely to be a knee jerk reaction and the needed conversation falls apart and that is to write a letter. By doing this you can take your time to set out what you really want to say, get the words right and make sure that it is only out of concern for both of them You may write one letter to both of them or, if you feel it appropriate, a letter to each. Again you will need to decide whether you leave them to read the letter/s or stay in the room while you do. However you choose to do it, it will be hard on you both but unless some honest discussion is started somehow, you won’t get very far and their situation may get worse as your Mum’s Parkinson’s progresses. It may be possible to open the conversation with your Dad in a low key way ie next time he says your Mum has given up or is not trying ask him why he thinks that, it may give you the chance to explain it’’s progression of the Parkinson’s not her being difficult. It might be easier if both of you were visiting - a bit of moral support.
Incidentally I am assuming from how you wrote your Mum has no cognitive problems as that could put a different complexion on things. Even if she is cognitively well she may not see the changes in herself or understand why her husband is getting so frustrated with her, to her how she is may just seem normal and not see that it’s changed. I know that sounds ridiculous but because progression tends to be slow it can take time to realise that you are not doing as well as you were 6 or 12 months ago and that can be hard. There may be an element of denial which will only add to your dad’s frustration.
I’m sorry I can’t offer anything concrete, I’m doing a lot of second guessing here but can only say it as I see it based on what you have written. Hopefully something in this will resonate or maybe change your perception a bit and I hope it is not too inaccurate. - however I always try to write an honest reply and trust you will read this with that in mind.
Let us know how you are getting on and if you have any questions please do not hesitate to come back to the forum.
Best wishes
Tot