I think it is realistic to make a difference between the writers and the characters they are writing. The characters can know only a little, but the writers should know everything, in order to have a complete overview and to be able to take the right decisions for their characters. Writing a story together with several other people means that all the writers should strive into the same direction, not write one against the other, so all should have the same informations.
And yes, I read all bios, first when I join/ they join in order to make a connection with my characters, then before/ when writing with them, to check out certain useful details.
This doesn;t mean, however, that my characters would know what I know.
This. I like to read other characters’ bios to pick out information that my character WOULD know, such as instances where they would have come across each other, or obvious personality traits that stand out. I especially read appearance, since it’s nice to know what your character is looking at. Of course, I don’t use information my character wouldn’t know in an rp post. But, if I’m writing a post, I would probably have the app open in another tab to check on information so I don’t type out, say, “He looked up at the other boy” when the other character is actually shorter than my character.
It’s also just fun to read what other people come up with for characters. Sometimes I’ll just sit in the app section and read through them, smiling like an idiot because I just love characterization.