Hello Rainy and Welcome
I think your role in this is limited. Your parents are making decisions that they feel are the correct ones. I think you could go to them and tell them that you are concerned, for their welfare, for Kiddo, and for the family. You could ask them if they want your help and your feedback. I agree with RB that you could suggest therapy, for all concerned. You could also ask if they want your help to locate support and resouces.
If they are not open to your help I think your option would be to limit contact where Kiddo is around. The other option is to ask your parents to withdraw you as a guardian or responsible for Kiddo, if they pass.
However concerned you are (and the situation is indeed concerning) it's your parent's responsibility to handle and to resolve this situation, as long as they are not being abused themselves. If you believe your mother, for example, is not competent due to age for example to make adequate decisions, this would be different; this would be considered abuse. But if you acted to involve authorities, this could create even greater problems.
Bottom line you're concerned about your parents, and everybody can understand this. You are motivated by love and care. The thing is as long as your parents are competent and their care of Kiddo is legally adequate, your decision-making role, as I see it, is limited. You would be limited to suggesting and supporting them, which I would assume you are already doing.
I don't know if others suggested this, but maybe your parents would be open to posting. All of us here were in their shoes. Maybe they might consider reading and posting. It's often easier to hear "strangers," people outside of the family who share a common plight, who don't know you and who you are unlikely ever to meet.
