To answer your question, it’s because none of the Sohma parents knew about the curse before the children were born so their reactions are not unrealistic

I can totally understand Kyo’s father bad treatment of Kyo though i don’t condone it but the cat has a second and is looked down, harshly judged, mistreated and ostracized along with his family by the entire clan including the zodiac so his father blaming him to escape the guilt for causing his wife to commit suicide is very realistic since it was pretty normalized by the clan, the fact that Kyo’s father wasn’t accepted by the family is what drove him to Insanity, he is trash but his issue is so complicated and he is also a victim like he is wife and let’s be realistic and honest with ourselves, no one would be able to handle that in real life and frankly Kyo’s situation is so extreme that you just have to feel sorry for the entire family

As for Isuzu’s parents, they are the worst and I have zero sympathy for them

What did they struggle from again ?

‎‏Yuki’s mother was literally abandoned by her trash husband and is the only one who had two zodiacs kids who she couldn’t even embrace and not just one

‎‏Momiji’s father was forced into a difficult position where he had to choose between keeping his wife sane and choosing his son

Ren is just so over the top that I can’t take her even seriously but she struggled and was treated badly by the Sohma’s like Kyo’s father

While they are considered the worst, I do appreciate their honesty about their hatred for Akito and Kyo, it’s better to be open and abandon your kid if you can’t stand them

‎‏Mental illness isn’t enough to justify Rin’s parents treatment towards Isuzu and they took it to a whole new level, was there a need for them to subject her to all that physical abuse, beat her up on daily bases, lock her up in a dark a room and deprive her of food and give her all those injures and bruises in her body, they treated her as if she was born as the cat or the cow not to mentioned that they lied to her and went from loving parents straight to physical abusive, there is a reason why Isuzu is the most mentally broken character and why she has the worst PTSD and that’s because she believed that her parents truly loved her unlike the rest. Takaya gave all the parent good reasons for being so toxic and horrible but made Isuzu parents seems like monsters, they don’t make any sense at all and they were just ungrateful, all the other bad parents struggled more than them, their daughter is a horse, an animal that is considered beautiful by most humans, Haru is a cow, Kisa is a Tiger, Ayame is a snake and Yuki is a rat, it would make more sense if Rin was one of those or the cat but their reaction was extremely unbelievable and over the top

I talked to people and I realized that they shouldn’t be in jail because life is not a fairytale and Rin would be so depressed about it