Yesterday something occurred to me (not sure if this had been discussed before, so forgive me if it has... ) and that is that I wonder if CD and LF were killed because KM and BS wanted their van. Then, when they tried to drive off in it (or, one in the truck and one in the van) they found it was flooded/inoperable so they had to leave it there.
I've been wondering about that, as well.
IMHO, we can reasonably assume all three victims were robbed (wallets, etc) because if they were not, they would not have been so hard for RCMP to identify (evidenced by RCMP asking for the public's help to ID the victims).
One thing that has never made sense to me was burning their truck so close to the professor's body. My current theory on that is that after the van murders, they headed off the Alaska highway at about the only road they could, toward Deese Lake. Their truck was old, so I'm wondering if it was started breaking down, leaving them trapped in the area - and area where they'd just committed two murders (I know Dease Lake was a long way from the van, but with so few roads and such sparse population, it's as if they were nearby, for these purposes).
I wonder about that van, too; perhaps they were after it as well, and it didn't start, as you say.
All this makes me wonder if they committed a crime back in their home area (perhaps as yet unlinked to them by the police, but the two suspects thought otherwise), which might explain their apparently precipitous departure from Port Alberni, and desire to change vehicles.