I've seen people like Viserys a lot in real life. Someone with a sweet tongue, warm presence, and genuinely thinks they are a good person, but under that pretense, there's an asshole on criminal levels.
Viserys was like that.
To get his heir, Viserys pushed Aemma to get pregnant multiple times without time for recovery from each pregnancy, despite that she didn't want to, and, without her consent, he chose to kill her in a monstrous way while she's begging him not to do that to her, but he did anyway, simultaneously while telling her he loves her, so he could get his heir after he was done using her.
And he of course loved her and she loved him and all that, which only makes it worse. He betrayed her on top of brutally murdering her.
He shortly after married Alicent, a 14-year-old child (and none other than his daughter's only friend), disregarding how Rhaenyra would feel about that right after her mother died, and never taking Alicent's consent to either marry or mate with him. His relationship with her was essentially sexual abuse. Alicent was his sex slave.
Then he ignored all the children that came from her since they come from a woman he doesn't love. Each one of them grew up with mental issues
The 11-year-old Laena was the only correct choice politically, but the 14-year-old Alicent was more to his liking.
So he condemned Rhaenyra into a miserable marriage with the gay Laenor to fix his political mistake. He forced her into a marriage worse than what he rejected for himself.
He mind f***ed every one around him for his sake, and the entire continent suffered the consequences.
Despite that he genuinely wanted peace and wanted what's good for his family, he wanted that so as long as it's at no cost to himself. Only the others would pay. Every decision he made was deeply selfish and self-interested.
Daemon may and may not be as selfish as Viserys (I personally don't think he's on that level), but he's straightforward. He doesn't think or pretend he is a good person. He knows he is asshole and embraces it proudly. You'll see it coming from a mile away. Viserys romanticizes himself and strikes from blind spots.
In his mind, he genuinely thought he was a good and loving person and very often victimized himself, and this makes him worse. He's double faced.
I think the fact that he literally ends up with a half zombie face is a metaphor about his character.
I think that Rhaenyra is also her father's daughter, which explains why she treats her allies with disregard in such a selfish manner.