they record their own vocals; in an ask i answered not too long ago i linked an ena card story where she explicitly goes to a karaoke booth to record her vocals, mizuki and kanade also have an area convo wherein kanade talks about how they picked mizuki to be the lead vocal in one of their new songs, theres a convo in a card story too (cant recall which) where mizuki was like “fufu, give me some praise for singing mafuyu’s lyrics so well!! >:3c” haha. i don’t recall them ever mentioning kanade uses vocaloid but i wouldnt be surprised if she had knowledge of the programme tbh