Either way I lose

This is my last week working at the daycare (yay!) and I am off tomorrow. I had planned to clean my house and perhaps go submit some more job applications. My mother sent me an email saying her and my dad have eye appts and want to come for lunch. I am so emotionally fragile right now and am really in no shape to deal with her. Since finding the info on Narcissistic Personality Disorder (npd), my whole world has changed. I now know beyond a shadow of a doubt that things will never improve and I will never have the kind of relationship with my mother that I have always desired. I am slowly coming to grips with the reality that my mother will never love me and it is devastating to say the least. At the same time, it is also very freeing and I have come to realize that the only way to protect myself is to have little or no contact with her. Of course she has no idea what I discovered about npd and would never in a million years admit that she has it and so she has no idea how much things have changed between us. The thought of having them in my house and watching them pretend to be loving grandparents makes me physically ill. My dilemma lies in deciding whether to protect myself or allow them to come so that they cannot claim that I am keeping John from them. They act very loving towards John (everything is an act with them) and he is obviously too young to see through their manipulations. I want to shield him from the truth which he is too young to comprehend and I want him to have happy memories of his grandparents. So do I suck it up and bow at her altar as I have been trained to do, or do I put myself first for once?