Everything on the family page that is not explicitly OOC information (eg, join date, etc) is considered fair game for IC information.
That is not to say that it must be treated as entirely canonical. If your RP for one of your adventurers is that they are a bastard offspring of one of your nobles, that the noble has never even heard existed, then that's perfectly legit, but it doesn't mean there couldn't be rumours of the connection to the family.
Remember: There's a difference between the things someone knows, and the things they think they know.
