LET ME TELL YOU ABOUT HOMESTU- Fuck, you know a lot about it anyway. Is Calliope actually Caliborn'ssister? There is a rumor that she isn't.

She is not, cherubs don’t have real siblings stated by both Calliope and Caliborn. Calliope called Caliborn her brother to relate to the kids and Caliborn started referring to Calliope as his sister since everyone knew who he was referring to and because he didn’t like her name to begin with.  Also since hearing their other half’s name put them to sleep it was just an easy way to avoid saying one another’s names.