According to this question, both μ's and Aquors are real life groups.
So, I am wondering what other groups that are mentioned in Love Live! School Idol Project and Love Live! Sunshine!! are also based off real life idol groups.
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In Japan, they are generally called as seiyuu unit (Japanese Wikipedia) when a music/acting unit (group) consists of voice actors. For a special case where a group also works as a real-life idol, it is called seiyuu idol unit.
According to the Wikipedia, there are 3 units, but only 2 are seiyuu idol units: