Detective Conan - Vol. 24 Ch. 235 - Within the Darkness

[MangaDex]

 

[Herocus]

Oh? You're approaching best girl? Instead of knowing she's taken by MC, you insist on ruining my ship and approaching best girl? So, you have chosen death.

 

[mangagon]

huh? why he called the older womam "mother-in-law"? should not he call that mother?

 

[zerio]

Man, it's always amazing how Kogoro always find an explanation for the weird things that Conan found.

huh? why he called the older womam "mother-in-law"? should not he call that mother?

This is a typical mistranslation.
The word for step-mom and mother-in-law are the same in Japanese, so you need the context to correctly translate this.

And as you said, he should have said "step-mom" on the first page.

Meanwhile, it's correct for the step-mom to call the grandma "mother-in-law" on the later page.

 

[Sonaldo]

Oh? You're approaching best girl? Instead of knowing she's taken by MC, you insist on ruining my ship and approaching best girl? So, you have chosen death.

Haibara didn't appear in this chapter tho