stpe mom's and holidays

Is it hard planning holidays with your step child. for the most part we do get to see my step child for holidays but mom is so inconsistent and they never did a holiday schedule in their order so my SO always just goes by what she wants and it totally leaves out my family being able to see my step child. what sucks more is that mom's ex husband gets time for holidays and my family has to go without. my family tries to include us so much and my step child as well because my nieces and nephew love my step child and they just never get to see my step child so holidays are almost the only time they can and it always works out that my SO only has his child when his family can see his child and then has to leave or when my brother has his kids we don't have my SO child because his child is with her ex husband. it sucks when holidays come around because of this.