One thing we're working on with His Highness lately is the concept of personal space. It's necessary, since we all want the new baby to survive until he's old enough to defend himself. But it is rather unfortunate timing. We have to try to word things sensitively so as not to create a feeling of personal rejection...
"We do not smush our brother."
"Please get off of your brother."
"Please unwrap your octopus body from Mommy."
"We do not poke our brother's eyes."
"Please give Mommy/your brother room to breathe."
"Mommy needs a personal bubble."
"I love you, but I need some space." (sounds like I'm breaking up with him, poor kid)
It'll catch on eventually...