1) I consider Chika trying to slap Touko to be an overreaction. But she is absolutely in her right to not trust Touko and her mom
2) She's angry because her baby was momentarily lost, due to her brother's inability to keep her baby safe in his arms. Worse, the baby is in the hand of someone she doesn't trust, and so she fears the worse.
3) Again, she specifically asked her brother because she didn't trust the others, she explicitly said this in this chapter. It didn't matter that nothing happened in the end to her baby, what mattered her brother failed to keep her baby to himself while she answered her phone. And what's more she even lashed at her brother for not understanding how she felt, she rightly pointed to him he couldn't understand her because he didn't have a child of his own. Touko wasn't his child, he didn't rear her since her infancy, he barely knew her maybe a month or two. He didn't made a baby of his own blood with a partner either. He didn't understand why his sister, a parent, was so fearful of her baby in the hands of a stranger whose intention she didn't know of and was suspicious of. Again, all of this are explained in this chapter.
Again, Chika trusted her brother because she knew him for years. She didn't know Touko and Miyako at all, and had no reason to give them her trust, in fact her gut feeling made her wary of them. Touko and Miyako being Hiroto's family a reason to blindly trust them is absurd. It's not because you trust someone that your family will automatically trust that someone, they can be skeptical (especially when you are the naïve/too trusting kind). Again, it was an error of Hiroto to not be at the baby's side at all times, since he accepted to keep the baby, it's not Touko's responsibility, Hiroto can't just transfer his responsibility to her, he was the one who got entrusted the baby, because once again Chika didn't trust his "family". And guess what, her gut feeling was right, last page showed the mother smiling. What kind of person would smile like that in that situation?
Finally, what's your problem? I've been arguing with you in good faith and respectfully, but you can't even extend that to me.