Feeling Lost

I know everyone's journey is different. But the more I read it seems they are very much alike. I am feeling so guilty, I feel like I am running away from dealing with my mom and her dease. I live about an hour away from my parents and work full time. Unless there is an emergency I can only go down on the weekends. My dad does not like me driving at night❤️. Which leaves him as the main caregiver.
This is putting such a strain on him. But he has rejected the idea of respite care. Im confused on the stages but I think mom is pretty advanced. The main issue is that both my dad and I get so frustrated with her. I think our frustration comes from PTSD from how she was been my entire life. I stayed at home much longer than my brother but somehow I think mentally he has always taken more of the mental abuse. Well him and dad. Abuse may be too harsh of a word. But she has always been narcissistic and controlling. My brother and his family are going through some rough medical times themselves right now. Which means he is not available very much either. My dad and I loose our temper and snap at mom and we dont mean to. I feel guilty when I do and I know dad does as well. I think this disease makes him feel powerless to help her and he is getting overwhelmed. She has always been bad about bringing up what we do wrong... especially with my brother and dad. I have always gotten a taste where and there. Mom has always held grudges and the times she feels someone has slighted her.
I'm sorry this is so long. Do ya'll have any tips or tricks on how to control our trained response to her? When she futzs with pills and drops them and loses them. When she says she didn't take the pill but she must have or dropped it. When she takes so long to come to the table because she is doing whatever else she wants to do.How do I play monkey in the middle? She always says I take his side... which I dont deny, our thought processes have always been similar.
Thank you for reading this rambling and any ideas on how to combat this are very much appreciated. As a quick aside here... if it wasn't for dad I may have gone no contact way before the disease.