Back Story: My sis is 13 years older than me, we havent ever gotten along for many reasons its honestly a 50/50 blame fight we were both in the wrong throughout the years.My Dad passed away oct 25,2008 leading to my Mom moving in with FI and I. Mary (my sis) moved to alaska in 2002 and never visited. When my Mom called her to tell her my Dad has stage 4 lung cancer Marys only responce was "Mom its 7am can I call you later". In the 7 months my Dad was sick she never called to check on him or Mom. In the year since he's passed she has called twice to talk to Mom. Mary moved back to Michigan last sat. Mom cooked a giant dinner for sunday after inviting them saturday and them accepting. Mom spent over $150 and literally all day sat/sun cleaning and cooking. Sunday 5pm comes around and the rest of my sisters show up without Mary and her 16 year old daughter Tiffany. Apparently they had all known all day sunday Mary and Tiff werent coming. Mary was mad Mom moved in with FI and I and didnt rent an apt with her instead. Now my Dad's 1 year anniv of being gone is next sun and Mom wants a quite dinner without drama. So she told me to plan it. Am I wrong that I want to invite all of my sisters without inviting Mary and Tiff because Im worried it will hurt my Mom on a already horrible day for her if they chose to just no show like last week. Mary is a 40 year old drama queen who literally starts fights and if you argue back she runs out of the house crying and swearing you will never see her or her daughter again. I dont want my Mom to deal with any of this or worry about it on her day shes dreading already so much.