User blog comment:CoolJazzman/Uryu "Last Living Quincy"?/@comment-1760658-20130701013709

Personally, I think he's just lying. He's that clever at manipulating many people.

From their expression, it seems that the Ishidas aren't well known within the organization. Which would explain why they're all so shocked at this so-called nobody becoming Yhwach's successor.

It's most likely he DOES know about Uryu's father (since he killed his wife and Uryu's mother), but wants to keep that "vital" information between him and Uryu for now.