It's all about name confusion, but the jokes depend a bit on the Japanese syllables used for the names.
Meiling's name is pronounced "Meirin" in Japanese, so only differs from "Eirin" on the first syllable.
"Sakuya" and "Kaguya" differ only slightly more; if written in kana, "gu" is just "ku" with a voice mark, so aside from that it's just the first syllable again.
"Kisume" and "Yamame" aren't all that similar, but they both use katakana for their given names, which makes them look similar: compare "ki"/"ya" (キ/ヤ) and "su"/"ma" (ス/マ), though this depends a bit on the font used.
...and, of course, the Aki sisters have completely different given names, but people always confuse the two anyway.
Nah, she's juste being her usual self, if we refer to her general behavior in Rapattu's works.
Minoriko-chan?Thanks for all your hard work!Huuuh?So you are all confused, you ignorant people!In truth, this incident was caused by the gods of autumn!It resulted from years of hatred over the question, "Who are the Aki sisters?"Well, it's about time we go home.You thought it would be a cute Minoriko-sama?
Too bad, it was just Shizuha-chan!