Title: ヤンデレに主導権を握られるオナニーボイス / Taken By Her Yandere Initiative - Masturbation Voice
Circle: CracK Pot
https://www.dlsite.com/maniax/work/=/product_id/RJ100336.html
Title: 勉強しないあなたに妹が優しく危機感を与えてくれる音声 / Little Sister's Inspiration To Study By Gently Reminding You Of Danger
Circle: 自己啓発の最果て / Ends of the earth
https://www.dlsite.com/maniax/work/=/product_id/RJ178931.html
Title: 無防備なフリして誘惑するいもうと / Love Whisper - Younger Sister 04
Circle: MooNSHINeR
https://www.dlsite.com/maniax/work/=/product_id/RJ063524.html
Links are dead, uploader is useless, so maybe someone else could share.
Title: 明るく元気で甘えん坊ないもうと / Love Whisper - Younger Sister 01
Circle: MooNSHINeR
https://www.dlsite.com/maniax/work/=/product_id/RJ061291.html
Post exists but uploader is useless.
Title: 妹の風邪をうつしてもらおう / Let's catch sister's cold
Circle: everestpeak
Links:
妹の風邪をうつしてもらおう (RJ059168) - https://www.dlsite.com/maniax/work/=/product_id/RJ059168.html
There are mp3 or WAV formats, but it's not much important.
Title: 妹の側に居たいから / I Want to Be on Sister's Side
Circle: everestpeak
https://www.dlsite.com/maniax/work/=/product_id/RJ088083.html
Because the only uploader is useless.
Title: 囁きシリーズその禄~超耳元であいしてる~ / Whisper Series 6: Love is in the Ear
Circle: あぐふぐヴェッチャーズ / Agufugu Butchers
https://www.dlsite.com/maniax/work/=/product_id/RJ123809.html
Title: 珠美のはじめてえっち~お兄ちゃんとしたいんだもん~ / Tamami's First Time: I Wanna Do It With Oniichan
Circle: plasticwater
https://www.dlsite.com/maniax/work/=/product_id/RJ120275.html
Title: 脳天気な妹は大好きなお兄ちゃんとイチャイチャする
Circle: Aボイス
https://www.dlsite.com/maniax/work/=/product_id/RJ136286.html
since all the links are dead, maybe someone could share this?