(To once again correct my goof, Joseph's last name back in the thread was Williams, which means Jon's would be too right now.)
Jon's school day went pretty much the same as usual until the end, when he went home. And it was the wrong home. He considered just following Joseph, but then did what he'd guessed he'd have to do: make another wish. "I wish" he said while clutching the stone, "that I knew everything I needed to know to act like I was really Joseph's brother."
"Oh shit" he said as the knowledge filled his skull.
"Jon?" asked Joseph. "Were you talking to that rock?"
"Oh, just a little nervous" he replied.
"Yeah, I can understand" said Joseph. "You've got that big date with Zoe tonight. That's what you're nervous about, isn't it?" He winked. "Let's go home" he said.
"You've got that right!" replied Jon. "Though not nervous in the way you think." Zoe was his sister, at least before the rock changed reality. He couldn't date her! "There's something I have to do. Not related to the date... but it's hard to explain. Okay? I'll see you later, it shouldn't be too long."
"Okay, be seeing you!"
As Joseph left, Jon considered his options. Try to wish himself out of this mess--wishing himself out of Joseph's family was probably impossible, but he might be able to wish away the date. Get some advice from Karyn--she had gone home but surely he could find her. Tell Zoe what's going on--she might even believe him. Or go on the date with Zoe, and use the rock to get out of any sticky situations....