In all honesty even when faced with absolute proof it is not unusual for family and friends to still deny the evidence. This has been the case with many serial killers/murderers families and you can't blame them, imagine finding out a person you loved and cared for, whom you considered a kind caring person had committed violent offences. You basically go through the same stages of grief but not always ending up at the final stage of acceptance.
Questioning as to if BRE had access to other white commodores doesn't sound out of the ordinary to me and certainly doesn't rule out having found other evidence in the already searched vehicle, it is simply good police work, if presenting a vehicle to a jury as the vehicle that was used in a crime the last thing you want the defense to claim is that "no, the defendant owned/drove this vehicle" which could put doubt in the minds of a jury. they are simply tying up all loose ends.
Lack of evidence at the Madora Bay property would only be a level of concern if this was known to be a place where the murders occurred, as theorized it's more than likely the murders took place a lot closer to the abduction point and bodies disposed off shortly there after.
keep in mind a lack of evidence is certainly not an indication of non guilt. DNA, geographical location, same vehicle identity as fibers found on a body, relationship break downs around the times of the attacks are all pointing to the alleged having committed the crimes. Then there is non public evidence, the KK victim (witness) and anything else the police have found or have had phoned in since the arrest. At this stage from an outside perspective there is a lot more evidence to suggest guilt rather than innocence.
I cknow you being someone close to BRE and/or the family have doubts and I can completely understand this, I just hope you too can understand why some of us feel the way we do.