They're basically side stories that vary in terms of spoilers. They are canon, however they're not necessary to be read for the Main Story.
All of these were first serialized in the LalaDX Magazine, after that they are then sold as their own books. Because of that, not all of these have ISBN as they haven't made it to the solo book format.
The serialization of this manga started on August 20, 2015 and came out every other Friday. The manga was mainly centered around the cast's daily life as an idol.
Which, in the past before August 1, 2017 you could read the most recent two chapter and the first for free on hanayumeonline.
However as of August 1, 2017 the manga started being hosted on Hakusensha's Manga Park (マンガPark). The mobile app is free to download. To read, Hakusensha provides 80 free coins twice a day and chapters cost 20 free coins to read. This free coin mechanic only applies to the mobile app.