The family I work for is in severe denial about their mother's health needs. How do I talk to them?

I have worked over a year for this family and through out time Ive noticed that when we come for Dr check ups the Dr would ask me the caregiver about the clients health. When I would state something that the family thought I was lying about, they would blurt out and say something like, "my moms not like this" and stay in denial about the mothers severe health situation. I have also run into other circumstances when doing my work and then reporting what has happened in the time I was working the would not believe me when I would inform the that the mother refuses to walk to the dinning table to eat breakfast or that she refuses to get up off the couch to use the restroom. Ive also stated things like she is loosing her ability to know and remember how to stand, get into a car, get out of a car and how to feed her self. When they saw me assisting their mom to eat, I got ridiculed for doing my job. They inform me that their on can eat on her own. which id true for 40% of the time. There are times when she demands that someone has to feed her/ Or she cannot find her food and asks for help. Ive personally sacrificed so many parts of my own life for my client and I can no longer deal with a family who lives in denial. The safety and well being of this human being means so much to me and that is why I have stayed as long as I have. But I can no longer put up with the BS non sense and drama atmosphere that this family has created for the caregiver team. How do I go about leaving amicably so no feelings are hurt between all parties involved.