The word abused is so overused in this story. As a victim of child abuse myself, I feel this manga mock me. I grew up fine and not stupid, despite years of mental and physical abuse from the very own person who supposed to love me. But the author really did the twins injustice for making them so stupid.
They're not stupid, it's just the basics of a toxic relationship. Kudos to you for having the mental willpower to withstand that, it's very admirable, but most people are tricked slowly over time into that toxicity. Plus, they were forced to live as babies so i think that would also regress your mental capacity, due to your body's incapabilities you would usually have as an adult.
Me and my siblings were also abused growing up and the abuse has affected each of us very differently. It caused my little sister to act out her frustrations at school, it caused my little brother to become so timid and scared to the point where he won't even sit in the front seat of the car because he's afraid to be beaten if the driver was to get upset. It caused my other sister to develop trust issues and think of it as her responsibility to protect us. Don't say that they're stupid. They're far from it and the abuse they endured was awful. Every day they were starved, beaten, and disparaged. That affects how someone views themselves and those around them. The twins are far from idiotic, they just can't bring themselves to trust others.
I agree..they have a child like appearance but remember? they have a 25-year old minds ..yet, they act and think as if they are still children who can't handle their emotions .. well, when you are already an adult... even if you are abused, you should know or think of ways on how to overcome your problems .. Well, I don't care if I am hated here ..I am just expression my frustrations here also

you know these kids are pretty frustrating for supposed 20 year olds