My stepmother demanded to know who was in my father's room when he was very sick. She badgered him to the point that he was weeping. I am very uncomfortable with the dynamic as her son is an attorney and has POA over his healthcare decisions and likey his estate. I don't think he can be objective given that we have witnessed my father's fear, duress and changes when she comes around. To badger a very old 86-year-old with pneumonia who just had a stroke is heartbreaking. I love my dad and I don't like the way she (my step mother ) treats my him. If she loved him then she would encourage him to have a relationship with his kids.
Lots of reasons why this isn't clear thinking! "If she loved him" assumes that loving someone means this, that or the other thing. Loving someone might mean that you want him all to yourself. Or her way of loving someone isn't the same as the way you love someone. Besides, maybe she doesn't like his kids in the first place, and she thinks she'd rather not put up with them whether she loves him or not. A relationship also has many meanings. My relationship with my father was much different from the relationship my friend had with her father. I liked to go out to meals with my parents, and talk with them often, but she couldn't stand her father and thought that talking to him on the phone once a month was quite enough.
Your stepmother appears to be a nasty person, and I'm sorry you have to put up with her. Or do you? Start thinking out of the box. Maybe she only gets to see him when someone is supervising. Or maybe you cut off contact with her altogether. Plus, it may be none of your business and you should back off. If you can talk with his doctors, tell them that stepmother's treatment of dad concerns you, and ask if doctor can do anything about it, since it's causing dad emotional stress that isn't good for his health.
Good luck with all of it, and keep in mind that sometimes we have to leave the scene in order to preserve our own sanity.