Sadly, I think this quite of backstabbing is quite common and in my own experience, it breaks families apart.
My sister, who is a couple of years older than me, has mild learning difficulties and suffers from anxiety. She has never married, has no children and she always lived with my mum and dad - being supported by them (often financially, although she has always worked part-time), eventhough quite capable of living independently. I felt she took advantage of their generosity, but it was their choice and I had left home at 18 and never gone back.
My parents were worried about what would happen when they were gone - especially since I lived a long way from them, with a family of my own. So I agreed with my parents, when I was still in my 20s that their estate would pass to my sister when they died, for her lifetime, and then her estate would pass to me on her death (or my children if I pre-deceased her) so everything stayed in the family - even though the amounts we are talking about are fairly modest in the big scheme of things. Don't get me wrong, an inheritance would have been useful, as we are not made of money, but I wanted my parent's minds to be easy.
Part of this understanding was that I would always be there to take care of things for her, which I was happy to do, and that she took on the practical care of our parents, as she lived with them, was quite capable and unlikely to ever leave home. Obviously, this would have been reassessed if circumstances changed.
We were all always happy with this arrangement - my parents were reassured, my sister was happy to take on most of the day to day care, and we all knew where things stood. I never once regretted my decision. She is my sister and I loved her.
Then, our mum died 6 years ago, and dad died within eighteen months of her. Mum had been ill for a long time and it was not a surprise when dad went not long after. To give her credit, my sister was brilliant at looking after both of them, and I don't know what would have happened if she had not been there - even though I was there as much as possible. I am sure many if you know what it is like juggling work and family with aged parents when you live a long distance from them - it is a constant struggle.
When dad died, I went and stayed with my sister - I organised everything for her, so she could remain living in the house for the time being and, as executor, put everything in motion to ensure her future. The plan being to set her up in a flat, near where she worked.
Unfortunately, nothing turned out as mum and dad wished. In their later years, we had discussed putting the estate in trust for my sister, so she was not vulnerable, was secure and would not have to worry - but this was never specified explicitly in either of their wills, just informally between the four of us, with my sister's full agreement. At every stage, my sister was included in the discussions and we made sure she understood the implications.
However, once my parents were gone, my sister refused to co-operate. She was adamant that everything was now hers without any interference from me! It was impossible to set up a trust without her agreement and she told solicitors she was confused and thought I was trying to con her after all she had done! She even cried in her meeting with them and played the complete victim, while still expecting me to sort everything out for her. I was incredulous!
So followed over three very difficult years trying to sort the estate, with my sister obstructing at every stage and misrepresenting the wishes of our parents to everyone, including the rest of our family. It turned out that she had my parents paying for pretty much everything before they died and had told the rest of our family that everything was my fault because I had not agreed for her to come and live with me and my family.....never an option, as she would have driven us insane!
The whole experience took a massive toll on me and has caused an irrevocable breach in the family - I now have nothing to do with my sister and am only in contact with one of my cousins (who said to me recently that he did not think my sister always told them the truth! You think?). My husband and family found it very hard to see me going through all this too.
Sorry for the lengthy rant, but you think you know your family until it comes to wills. I would never agree to be an executor again. It is a thankless task and causes endless sleepless nights. I feel so betrayed by my sister's actions and she has blighted any happy memories of our family.