There is no evidence that supports the notion that Robin killed his wife, two daughters and youngest son. Evidence that he killed himself is equally hard to establish. There were fingerprints on the rifle, but none were identified as belonging to Robin. The only identifiable fingerprints belong to David Bain. While it is possible for Robin to have killed himself in the manner argued by the Bain Defence Team, it is highly unlikely, especially given the other factors surrounding the case.
Bryan Bruce's documentary The Case Against Robin Bain clearly spells out many reasons why it could not have been Robin.
The Bain Defence team's scenario is very unlikely to have been possible.