This is something that usually happens when someone dies. Conflicts with regards to properties arise especially when no will has been done. I've seen this happen to several people I personally know. My husband's cousins are still in that kind of situation right now. Their grandmother who raised 2 of her grand daughters died last year and she had no will made but she promised that the house they're living in belongs to the 2 grand daughters. Now the younger one is being kicked out of the house by the older one. There are more conflicts to the story but it's a bit confusing for me too so I won't elaborate any further. Maybe the point in all this is to always make sure you have an updated will at least every year to avoid family feuds due to property issues in the future.
The sister needs a real estate lawyer ASAP. If no will was left, the courts will get involved. It was mentioned that the sons and daughter are heirs and an heiress. If no will was left, don't count too heavily on that.
