Question regarding what I could only call a "Lifetime Deed"?

My grandparent's moved out of their home about 5 years back due to failing health. An acquaintance of the family began visiting them alot. She was having problems with her deceased husband's children regarding the home she was living in at the time. Out of the goodness of his heart my grandfather offered to let her live in their empty home, rent/mortgage free, for the rest of her life if she would help by sitting with and being a general caretaker for my grandmother and himself. My grandmother has since passed, but the woman only spent about 6 months helping, after that she flat out refuses to help. I do not have the "deed" in question in my hands now, but will in a few weeks. I do know that my grandfather trusted her and didn't feel it necessary to put the caretaker/caregiver stipulation into the contract he had drawn up, so in effect that part is only verbal, but it's well known between us and our family. She's also made mention at gatherings and such before to that affect as well on many occasions (showing gratefulness for allowing use of the home for her life in exchange for her caretaking services). It was only signed by the lawyers, himself and herself, even though my mother had at the time and still has power of attorney of my grandfather. My parents cannot get her to help at all with my grandfather, who we've since found out has Alzthimers(sp). She now has a boyfriend who she moved into the house. My parents informed her that he would have to pay rent/mortgage. She got angry and refused, but took her copy of the agreement to her laywer in hopes she'd be in the right, but her lawyer sided with my parents, telling her the agreement was for her and her alone, and anyone else living in the house would have to pay rent. My parents have only (verbally) told them he had to pay $200 a month, which I find crazy because rent for a house in that area is minimum $800 a month, (which would make him responsible for $400). I told them when I found out that they should have a lease drawn up and up his rent. Anyway, after her being angry with them for doing that, as well as her constant demands on my family to make improvements and upgrades to the house (none necessary, all asthetic) she's since gone and changed all the locks in the home. She swears up and down that there never was an agreement for her to help care for my grandparents. The home is still in my grandfather's name. What happens when he passes away and it gets put in my Father and Uncle's names, and eventually passed on to myself, my brother and my cousin. Is that agreement(contract) null and void? Just seems to me that legally a new property owner can't be forced to uphold an agreement, contractual or not, that was made with the previous owner. At the very least seems to me that when he passes my parents could draw up a new agreement. I know they couldn't legally evict her, but seems to me that just like when a rental property changes ownership and a new lease has to be drawn up, this is the same. Ideally if they do draw up paperwork stating she would now be responsible for paying "rent" (as the house is paid off w/ no mortgage), and she refuses, can they did ask her to leave? Also, since the house isn't in her name and she's only being "allowed" to live there and changed locks without the owner's knowledge or ok....does that make that agreement null and void??? Thanks!