My gran is a very deluded woman who has lived a terrible life. Married at 17 to an abusive husband, two kids with him before getting divorced then falling into an affair with a marked man with 4 kids of his own. From this encounter she fell pregnant, then purposely had another baby to prove to the neighbours that her first child with him wasn't an accident.
Her second children were now her little darling because they were her married man's children who she idolised despite him always going home to another woman. Her first two children who were teenagers by this time found themselves ignored and mistreated, and she continued this sordid affair with this married man- until his wife died, and he then moved in with her properly.
My father was one of the children from this second union, and him and his brother didn't find out the truth about his mothers life until he was in his twenties. My gran went out of her way to fake they were married, even changing her name via deed poll because he refused to marry her :(
She even emigrated with him last year to a rural country, away from her friends , grandchildren and civilisation. She took out a mortgage in her name to fund the move in her 70s to make him happy (she forced my father to co-sign for this)
Now they're in their 80s and getting to the age where they're getting ill. My grandfather has lung cancer, and is still smoking- as well as being a difficult bastard and my Gran panders to him and plagues the family with his over-exaggerations. He has had cancer for 6 years, but since day one he's been 'dying'- by that I mean that every week my gran stages an emergency and attempts to drag the family over at least once a month. Because of how she treated her older children, and because of the affair- they want nothing to do with her. My dad's younger brother feels the same way about his father too- so the burden has been left on my father. Since his dad got cancer he has been travelling to this country (6 hour journey) and at a great cost. MIL doesn't know the value of money and seems to think these little emergency visits are free- but a long weekend every month puts a massive dent in my father's holiday allowance (only gets 4 weeks a year, but his boss is quite kind and gives him a BIT of lee-way) and also his bank balance, as he'll spend at least 500 quid on the trip no matter what.
This is putting huge strain on my parents marriage. My mother would never begrudge my father a visit to his sick parents, but every time he ends up there- he's never bloody sick. Yes, he has cancer- but he's never 'dying' and it's never an emergency. The way I see it as that once you hit your 80s, you've got to die of something- and the way he has acted his whole life, he should count himself bloody lucky that karma hasn't hit him so hard.
He hasn't had chemo or anything. The doctors in Ireland have basically said it's not advancing at a slow speed, and at his age- treatment would probably wear him down even more. He's diagnosed with it, but it hasn't affected his life at all.
Irregardless of this- my Gran will phone up my Dad and guilt trip him into coming over to visit. I'm 20 with a DD of my own, and my Dad even has a go at me for not wanting to go and visit more- but I detest the man and what he has done to my grandmother. This naturally causes lots of arguments and leaves my mother in tears.
My mother has had a traditional evil MIL situation since she met my father and has never ever saw eye to eye with her- and my Gran is using their bad relationship to manipulate my dad into thinking that my mum wants them both to die as soon as possible 
I understand, my nan has had a terrible life and I sound heartless- but the whole family have given her opportunities to come back to the UK and live with us, and we'll pool together for a place- she doesn't want to come back without him...and naturally, he won't be coming back any time soon.
I'm sick of all of the phone calls, her constantly calling my father and manipulating him, putting the entire burden of costs and looking after them on him and painting my gorgeous saint of a mother to be some witch who wants to begrudge my father a visit to his sick parents.
Other family members have noticed the strain that my parents are under and have phoned my Gran saying 'if you put any more stress on [my dad] then you're going to have a divorce on your hands' - my Gran said quite bluntly that she didn't care, and wanted my father to move abroad and live with her.
To make things worse, I accidentally logged into my mum's facebook on the iPad yesterday and found numerous exchanges between her and her friends that her marriage was on the rocks because of the way my Gran is acting, and the tensions she is raising :( I'm gutted. My parents had a turbulent relationship, on-and-off, bouts of DV, but when I was 12- they put it all behind them and have been happy ever since...all until my Gran started acting like this.
I don't know what to do.
If I talk to my Gran, she'll tell my dad and it'll cause a fight. I was thinking of phoning up some of the families I know in their village who pop in for tea and take them shopping (I spent summers there as a teenager) and make them aware of the stress that she is causing back home, and just let them know that if my nan is calling my Dad over to visit and my grandfather isn't that ill- to try and persuade her not to...