@Hacete
Eh, I'll give Kotone, Chiaki and Nonoka a pass because technically they never met Daisuke's mom before seeing him crossdressing. They also did not know she'd come (she said it herself that she came to watch in secret), so it'd be more reasonable for them to assume someone that looks like female Daisuke to be the dude himself crossdressing and not his (absurdly young-looking) mother. Suzu should also get a pass for the second reason, since she's the first of the harem to meet Mama Goryou so first reason doesn't hold up. And like
@mage_goo said, the height difference is marginal enough to not notice at first glance. Sure they
love like him, but not to the obsessive degree of knowing every single minuscule detail about his body.
And chapter 169 has Kotone seeing Daisuke crossdressing in the waitress getup that's near-identical to his mom, so she has even more justified reason to make the mistake.
Not having enough pages for Mama Goryou to react to the rest of the harem aside, another missed opportunity for this setup is either Suzu or Asahi-sensei (who know what Mama Goryou looks like AND that Daisuke is an attractive crossdresser) realising her and awkwardly trying to hide from her the fact that her son crossdresses (extremely well).