In the beginning of Blackwell Deception, how is the ghost driving the boat? No other ghost in the series (with the exception of the Countess, who has special powers) has been able to touch solid objects.
Well, Jeremy could still make an actual phone call without a phone and Joey can mess with electronics/blow on stuff, so clearly they're not completely separate from the physical world. It would seem that ghosts have connections to things that were very important to them and retain some control over them. Presumably it's even stronger if that's where they died.
So it's pretty obvious that Frank Lyons was killed by the Countess, but how did his ghost gain a bit of the memories and personality of Joe Gould? Yes, Joe's ghost was trapped in the Countess' spiritual bond, but outside of that, there doesn't seem to be a clear explanation.