shortey
re the jack russell. 'they remembered afterwards that their son had always wanted one'. they were so desperate for proof, for it to be right, that they would remember anything. which kid didn't want a dog? i bet my parents would remember me wanting a jack russell if they were in the same state of near hysteria that those parents were in.
its easy to get somebody's sister's name. either plant somebody, or point at a small section of the audience and insist that one of them is Xavier's sister. eventually somebody will give in to the tension. then its like 'a lie that grows bigger'. once they've implicated themselves, they'll agree to anything.
i know somebody who 'became' a stage medium so he could make a TV programme debunking them. he didn't use plants, just the 'embarrassment' technique. this stuff works.