It would be difficult, all these years later, to ask YW directly, no doubt about that. But that doesn't mean it can't be done, it means legitimate ways of doing so have to be found.
Gran's lies were not called out in court. Evidence of JF and GD's lies consisted almost entirely of cross-examination of their lie about the time they were on the path. Their reasons for not coming forward sooner were pretty much skipped over at trial - they were asked, mumbled the usual "I don't remember" and then things moved on. JF was quizzed about cutting his hair, but that line of questioning ended up going round in circles.
It's almost impossible to believe - if the defence QC had pushed the question "why did you not come forward before the police television appeal?" whatever answer JF had given, the opportunity would have been right there to read out his police statement about his Gran telling him not to.
None of the information about Jodi's previous "disappearance" two months earlier, and the complete lack of concern on that occasion, came out in court. None of the family's tendency to cover things up from each other came out (I'm not casting any negative aspersions there - the absolute truth is that they did cover for each other prior to Jodi's murder - from each other, from the authorities, from the medical profession.) It took 8 years for me to find out the truth about these matters, and then to face the utter disbelief that none of it made it into the trial.
This is from memory, so the timings may be out a little bit:
JuJ's claim was that JF was with JoJ the whole afternoon until "sometime after 3.30pm" - she couldn't say for sure, because she didn't hear him leave. BUT, JuJ called the doctor at either 3.05 or 3.20pm that day (really sorry, I don't remember which) to cancel JoJ's regular home visit (for his mental health conditions) which was scheduled for 5pm. When she was asked why, she said it was because JoJ wanted to smoke cannabis, and the doctors had said he should not because it negatively impacted both his medication and conditions.
Let's just break that down. According to the statements, JoJ and JF had been smoking cannabis since "lunchtime." It could be that JuJ was wrongly quoted when she said "wanted to smoke " rather than "had been" smoking. But if JuJ was in the living room, calling the doctor between 3.05 and 3.20pm, how did she not hear JF leaving? He would have to have walked past the room where she had just called the doctor, the room where she sat in silence (doing some paperwork) until just before 4pm, when she went into the kitchen to start preparing dinner. More to the point, she is quite clear it was sometime after 3.30 - how did she know? In one statement, she suggests that JF is there when JoJ asks her to call the doctor, but according to JF and a statement attributed to JoJ, JF was long gone by then.
And why, of all days, was the appointment cancelled that day? It was clearly not an issue prior to that day - doctors' visits when JoJ had been smoking were not unheard of.
If the statement is accurate, and the appointment was cancelled because JoJ "wanted to (continue to) smoke", and JF was there when the request to call the doctor was made, did it not occur to JuJ that it was a little strange that JF left so soon afterwards? If the request was so that the smoking session could be extended (as JuJ seemed to be implying), why did JF leave almost as soon as the arrangement had been made?
It's important to understand, in terms of the timings here, that Jodi walked through the door no later than 4.05pm. There has never been any suggestion that JF was still in the house when Jodi arrived home from school.