Am I being unfair or selfish?

My parents have lived independently in a retirement community for the last 12 years. As of March, 2024, they transitioned into personal care which means they no longer have the responsibilities of shopping, meal prep, laundry, cleaning, etc… It has been quite the adjustment. My father, who has always been somewhat difficult and explosive has had some run ins with other residents. My dad has dementia but has always had the behaviors my mom claims are due to dementia; forgetfulness, confusion, agitation, etc… These are not new behaviors. My mom has some physical limitations but mentally, she is still fairly sharp. They have and have always had a contentious relationship. Very unhealthy communication and have not shielded me from any of their toxic behaviors. They are both only children and not much family to speak of. My brother recently moved out of state approximately 2 years ago. I am the only family to visit my parents regularly. They live about 35 minutes from me. I stayed home to raise my own children for 21 years. Now my children are grown and I returned to teaching the same year my brother moved out of state.
I feel the weight of the responsibility of being the only family my parents have to check in on them, accompany them to doctors appointments or hospital stays, intervene when issues arise with my dad, and make sure they have somewhere to go for holidays.
My mom has gotten more nasty with me in the last three years. She wants to vent about my dad’s behavior and the toll it takes on her. I respond emotionally but not violently or aggressively. She claims that she needs to be able to talk to me but that I can’t react. I have to remain calm and relaxed because she is too fragile for my emotions. I told her I am not a robot and if that’s what she needs, I can’t be the one she talks to. I also told her she can’t vent to me about my dad because it’s not healthy for me. I spent many years growing up hearing how unbearable my dad’s behavior was and I didn’t know this was unhealthy for me to have to listen to. I’ve since learned how to have healthy boundaries and I refuse to be my mom’s support group or emotional dumping ground. That’s my dad and she’s my mom and I’d never do that to my own children. My mom tells me how she can’t talk to me but can talk to my brother. I think she says it to hurt me. My brother has not visited them since March and he has not contact with his own children. He and his wife (second wife who has no children of her own) are apparently too busy to visit. Meanwhile I have two adult children that I see regularly, a husband who travels internationally for work, a full time teaching job but it’s up to me to visit and intervene when needed. I feel like there is so much expected of me and I’m resenting how my brother (our relationship is strained and we don’t really communicate because I’ve reached out but it’s never reciprocated) has zero responsibility. When I point this out, my parents defend him and talk about how busy he and his wife are. He is an associate pastor and she does payroll for a hospital. We all have the same 24 hours and we all prioritize what we really care about.
My mom just hung up on me again tonight when I called to let them know about what I’m doing to better equip myself as their power of attorney. She got mad because once again, she wanted to tell me about my dad’s latest problem with another resident and the toll it has taken on her. I became upset ( no yelling but the volume of my voice did increase and my tone became more emotional). She told me she is too fragile for me to respond or react and she just needs to talk about it. I told her I am not a robot and I won’t yell or be disrespectful but I’m upset about what happened to my dad; he was not the instigator in this situation. She said she can talk to my brother but not me and I responded with it’s easy to not react when you don’t have to do anything about it because he does NOTHING other than listen.
Am I wrong???